Methods and Systems for Treating Hypertension Using An Implantable Stimulator

ABSTRACT

A method of treating hypertension includes an implantable stimulator generating stimulation sessions at a duty cycle that is less than 0.05 and applying the stimulation sessions by way of the central electrode and the annular electrode to a location associated with the hypertension and within a patient.

RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 16/693,008, filed Nov. 22, 2019, which is acontinuation application of U.S. patent application Ser. No. 15/700,013filed Sep. 8, 2017 and issued as U.S. Pat. No. 10,518,082, which is adivisional application of U.S. patent application Ser. No. 14/805,355,filed Jul. 21, 2015 and issued as U.S. Pat. No. 9,789,304, which is acontinuation application of U.S. patent application Ser. No. 14/446,500,filed Jul. 30, 2014 and issued as U.S. Pat. No. 9,358,382, whichapplication is a divisional application of U.S. patent application Ser.No. 13/598,575, filed Aug. 29, 2012 and issued as U.S. Pat. No.8,805,512. U.S. patent application Ser. No. 13/598,575 also claimspriority under 35 U.S.C. § 119(e) to U.S. Provisional Patent ApplicationNo. 61/575,869, filed Aug. 30, 2011; U.S. Provisional Patent ApplicationNo. 61/606,995, filed Mar. 6, 2012; U.S. Provisional Patent ApplicationNo. 61/609,875, filed Mar. 12, 2012; U.S. Provisional Patent ApplicationNo. 61/672,257, filed Jul. 16, 2012; U.S. Provisional Patent ApplicationNo. 61/672,661, filed Jul. 17, 2012; U.S. Provisional Patent ApplicationNo. 61/674,691, filed Jul. 23, 2012; and U.S. Provisional PatentApplication No. 61/676,275, filed Jul. 26, 2012. All of theseapplications are incorporated herein by reference in their respectiveentireties.

BACKGROUND INFORMATION

High blood pressure (HBP), also known as hypertension, affectsapproximately one billion individuals world-wide. Hypertension isgenerally viewed as a bad thing if it persists for long periods of timeor is extremely high over a very short (e.g., hours) period of time. Theadverse effects of hypertension typically take many years to develop,but they include stroke, angina and heart attacks.

High blood pressure is traditionally treated with drugs. Unfortunately,not every patient who develops HBP responds favorably to such drugs.Many patients have severe adverse side effects. For others, the drugsare not effective for their intended purpose. Thus, there is a criticalneed for alternative methods and techniques for treating high bloodpressure.

Alternate techniques for treating HBP include electrical stimulation.For example, several proposals have been made to treat moderatelyelevated blood pressure using highly invasive methods such as vagal(part of the vagus nerve) nerve stimulation, spinal cord stimulation anddeep brain stimulation. It has been known in the past that one canstimulate the vagal nerves by invasively dissecting the major nervebundle and placing a spiral or enveloping nerve-type cuff around thenerve bundle. The nerve fibers are then directly stimulated by anelectrical field to achieve a reduction in epilepsy, heart-rate slowing,and potential blood pressure changes.

Currently, only nerve cuff-type electrodes or in-placement-typeelectrodes are used for nerve stimulation, other than in the spinalcord. These types of electrodes can potentially cause irreversible nervedamage due to swelling or direct mechanical damage of the nerve. Theplacement of these electrodes either around the nerve bundle or into theneural perineum also poses a significant risk. The electrode placementis usually performed through very invasive surgery which in and ofitself produces a high risk to nerve damage.

U.S. Pat. No. 5,707,400, issued to Terry, entitled “Treating RefractoryHypertension By Nerve Stimulation,” proposes implantation of anelectrical coil or cuff around the vagus nerve, which runs superficiallythrough the neck, and stimulation of the vagus nerve to lower high bloodpressure.

U.S. Pat. No. 6,522,926, issued to Kieval, entitled “Devices and Methodsfor Cardiovascular Reflex Control,” and several other patents issued tothe same inventor, describe devices, systems and methods by which theblood pressure is reduced by activating baroreceptors. The baroreceptorsare the biological sensors in the wall of the carotid artery thatindicate to the brain an abrupt rise or fall of blood pressure byresponding to the stretch of the arterial wall. In response tobaroreceptor stimulation, the brain reduces the pumping of the heartwith the consequential moderation of blood pressure. This phenomenon isknown as the body's “baroreflex”.

U.S. Pat. No. 5,199,428, issued to Obel, entitled “ImplantableElectrical Nerve Stimulator/Pacemaker with Ischemia for DecreasingCardiac Workload,” describes a method and apparatus for (1) stimulatingthe right and/or left carotid sinus nerves, (2) the right stellateganglion or (3) the epidural space of the spine with electrical pulsesin response to detected myocardial ischemia to decrease cardiac workloadas a method to protect the myocardium.

The methods described above are potent and are capable of, at leasttemporarily, reducing blood pressure in a patient. However, such methodsare highly invasive and have potentially debilitating or lifethreatening side effects. In general, it may be said that these methodsattempt to regulate blood pressure by directly changing the vital partsof the central nervous system such as brain, spinal cord, vagus nerveand carotid sinus nerves. The potential side effects of such adevice,—including nerve damage and paralysis—make the use of thesemethods unlikely except in the most severe cases where the high risk canbe justified.

Another alternative technique for treating HBP, and a host of otherphysiological conditions, illnesses and deficiencies is acupuncture.Acupuncture has been practiced in Eastern civilizations (principallyChina, but also other Asian countries) for over 2500 years. It is stillpracticed today throughout many parts of the world, including the UnitedStates and Europe. A good summary of the history of acupuncture, and itspotential applications may be found in Cheung, et al., “The Mechanism ofAcupuncture Therapy and Clinical Case Studies”, (Taylor & Francis,publisher) (2001) ISBN 0-415-27254-8, hereafter referred to as “Cheung,Mechanism of Acupuncture, 2001.” The Forward, Chapters 1-3, and 5 ofCheung, Mechanism of Acupuncture, 2001, is incorporated herein byreference.

Despite the practice in Eastern countries for over 2500 years, it wasnot until President Richard Nixon visited China (in 1972) thatacupuncture began to be accepted in Western countries, such as theUnited States and Europe. One of the reporters who accompanied Nixonduring his visit to China, James Reston, from the New York Times,received acupuncture in China for post-operative pain after undergoingan emergency appendectomy under standard anesthesia. Reston experiencedpain relief from the acupuncture and wrote about it in The New YorkTimes. In 1973 the American Internal Revenue Service allowed acupunctureto be deducted as a medical expense. Following Nixon's visit to China,and as immigrants began flowing from China to Western countries, thedemand for acupuncture increased steadily. Today, acupuncture therapy isviewed by many as a viable alternative form of medical treatment,alongside Western therapies. Moreover, acupuncture treatment is nowcovered, at least in part, by most insurance carriers. Further, paymentfor acupuncture services consumes a not insignificant portion ofhealthcare expenditures in the U.S. and Europe. See, generally, Cheung,Mechanism of Acupuncture, 2001, vii.

Acupuncture is an alternative medicine that treats patients by insertionand manipulation of needles in the body at selected points. Novak,Patricia D. et al (1995). Dorland's Pocket Medical Dictionary (25thed.). Philadelphia: (W.B. Saunders Publisher). ISBN 0-7216-5738-9. Thelocations where the acupuncture needles are inserted are referred toherein as “acupuncture points” or simply just “acupoints”. The locationof acupoints in the human body has been developed over thousands ofyears of acupuncture practice, and maps showing the location ofacupoints in the human body are readily available in acupuncture booksor online. For example, see, “Acupuncture Points Map,” found online at:http://www.acupuncturehealing.org/acupuncture-points-map.html. Acupointsare typically identified by various letter/number combinations, e.g.,L6, S37, which maps also identify what condition, illness or deficiencythe particular acupoint affects when manipulation of needles inserted atthe acupoint is undertaken.

References to the acupoints in the literature are not always consistentwith respect to the format of the letter/number combination. Someacupoints are identified by a name only, e.g., Tongi. The same acupointmay be identified by others by the name followed with a letter/numbercombination placed in parenthesis, e.g., Tongi (HT5). The first lettertypically refers to a body organ, or other tissue location associatedwith, or affected by, that acupoint. However, usually only the letter isused in referring to the acupoint, but not always. Thus, for example,the acupoint P-6 is the same as acupoint Pericardium 6, which is thesame as PC-6, which is the same as PC6, which is the same as Pe 6 whichis the same as Neiguan. For purposes of this patent application, unlessspecifically stated otherwise, all references to acupoints that use thesame name, or the same first letter and the same number, and regardlessof slight differences in second letters and formatting, are intended torefer to the same acupoint. Thus, for example, the acupoint Neiguan isthe same acupoint as Neiguan (P6), which is the same acupoint as Neiguan(PC6), which is the same acupoint as Neiguan (PC-6), which is the sameacupoint as Neiguan (Pe-6), which is the same acupoint as P6, or P 6, orPC-6, PC6 or Pe 6.

An excellent reference book that identifies all of the traditionalacupoints within the human body is WHO STANDARD ACUPUNCTURE POINTLOCATIONS IN THE WESTERN PACIFIC REGION, published by the World HealthOrganization (WHO), Western Pacific Region, 2008 (updated and reprinted2009), ISBN 978 92 9061 248 7 (hereafter “WHO Standard Acupuncture PointLocations 2008”). The Table of Contents, Forward (page v-vi) and GeneralGuidelines for Acupuncture Point Locations (pages 1-21), as well aspages 45, 64, 151 and 154 (which pages illustrate with particularity thelocation of acupoints ST36, ST37, PC5 and PC6) of the WHO StandardAcupuncture Point Locations 2008 are submitted herewith as Appendix D,and are incorporated herein by reference.

While many in the scientific and medical community are highly criticalof the historical roots upon which acupuncture has developed, (e.g.,claiming that the existence of meridians, qi, yin and yang, and the likehave no scientific basis), see, e.g.,http://en.wikipedia.org/wiki/Acupuncture, few can refute the vast amountof successful clinical and other data, accumulated over centuries ofacupuncture practice, that shows needle manipulation applied at certainacupoints is quite effective.

The World Health Organization (WHO) and the United States' NationalInstitutes of Health (NIH) have stated that acupuncture can be effectivein the treatment of neurological conditions and pain. Reports from theUSA's National Center for Complementary and Alternative Medicine(NCCAM), the American Medical Association (AMA) and various USAgovernment reports have studied and commented on the efficacy ofacupuncture. There is general agreement that acupuncture is safe whenadministered by well-trained practitioners using sterile needles, butnot on its efficacy as a medical procedure.

An early critic of acupuncture, Felix Mann, who was the author of thefirst comprehensive English language acupuncture textbook Acupuncture:The Ancient Chinese Art of Healing, stated that “The traditionalacupuncture points are no more real than the black spots a drunkard seesin front of his eyes.” Mann compared the meridians to the meridians oflongitude used in geography—an imaginary human construct. Mann, Felix(2000). Reinventing acupuncture: a new concept of ancient medicine.Oxford: Butterworth-Heinemann. pp. 14; 31. ISBN 0-7506-4857-0. Mannattempted to combine his medical knowledge with that of Chinese theory.In spite of his protestations about the theory, however, he apparentlybelieved there must be something to it, because he was fascinated by itand trained many people in the west with the parts of it he borrowed. Healso wrote many books on this subject. His legacy is that there is now acollege in London and a system of needling that is known as “MedicalAcupuncture”. Today this college trains doctors and western medicalprofessionals only.

For purposes of this patent application, the arguments for and againstacupuncture are interesting, but not that relevant. What is important isthat a body of literature exists that identifies several acupointswithin the human body that, rightly or wrongly, have been identified ashaving an influence on, or are otherwise somehow related to, thetreatment of various physiological conditions, deficiencies orillnesses, including hypertension. With respect to these acupoints, thefacts speak for themselves. Either these points do or do not affect theconditions, deficiencies or illnesses with which they have been linked.The problem lies in trying to ascertain what is fact from what isfiction. This problem is made more difficult when conducting research onthis topic because the insertion of needles, and the manipulation of theneedles once inserted, is more of an art than a science, and resultsfrom such research become highly subjective. What is needed is a muchmore regimented approach for doing acupuncture research.

It should also be noted that other medical research, not associated withacupuncture research, has over the years identified nerves and otherlocations throughout a patient's body where the application ofelectrical stimulation produces a beneficial effect for the patient.Indeed, the entire field of neurostimulation deals with identifyinglocations in the body where electrical stimulation can be applied inorder to provide a therapeutic effect for a patient. For purposes ofthis patent application, such known locations within the body aretreated essentially the same as acupoints—they provide a “target”location where electrical stimulation may be applied to achieve abeneficial result, whether that beneficial result is to reduce pain, totreat myocardial ischemia, to treat hypertension, to mitigate some otherform of cardiovascular disease or to address some other issue associatedwith a disease or condition of the patient.

Returning to the discussion regarding acupuncture, some have proposedapplying moderate electrical stimulation at selected acupuncture pointsthrough the needles that have been inserted. See, e.g.,http://en.wikipedia.orq/wiki/Electroacupuncture. Such electricalstimulation is known as electroacupuncture (EA). According toAcupuncture Today, a trade journal for acupuncturists:“Electroacupuncture is quite similar to traditional acupuncture in thatthe same points are stimulated during treatment. As with traditionalacupuncture, needles are inserted on specific points along the body. Theneedles are then attached to an electrical device that generatescontinuous electric pulses using small clips. Such electrical device isused to adjust the frequency and intensity of the impulse beingdelivered, depending on the condition being treated. Electroacupunctureuses two needles at a time so that the impulses can pass from one needleto the other. Several pairs of needles can be stimulated simultaneously,usually for no more than 30 minutes at a time.” “Acupuncture Today:Electroacupuncture”. 2004-02-01. (Retrieved on-line 2006-08-09 athttp://www.acupuncturetoday.com/abc/electroacupuncture.php.)

Recent research has reported the use of electroacupuncture (EA) for thetreatment of hypertension. Li et al., “Neural Mechanism ofElectroacupuncture's Hypotensive Effects”, Autonomic Neuroscience: Basicand Clinical 157 (2010) 24-30. Such report indicates that Chinese andSoutheast Asian medical professionals have long utilized acupuncture,and its potent and more standardized alternative, electroacupuncture(EA) to treat disease. EA is characterized in the report as beingadministered by a small electrical current through needles from abattery driven device.

The reason why acupuncture, including EA, has a depressor effect on sometypes of hypertension is discussed at length in Cheung, Mechanism ofAcupuncture, 2001, chapter 5, previously incorporated herein byreference.

In U.S. Pat. No. 7,373,204, issued to Gelfand et al., entitled“Implantable Device and Method for Treatment of Hypertension”, there isdisclosed a method and apparatus that treats hypertension withelectrostimulation of peripheral nerves. A pacemaker-sized device isimplanted in the fatty tissue of the patient, e.g., in the chest, andthen long leads, with electrodes at their distal ends, are tunneledthrough body tissue so that the electrodes reside at a desired location.In one embodiment, the desired location where electrostimulation isapplied is near the median nerve in the wrist of the patient, whichcorresponds to acupoints P5 and P6. Gelfand also recognizes thatacupuncture, including electroacupuncture, has been used to treathypertension. See, '204 patent (Gelfand et al), col. 3, lines 43-60.

To use a device as described in Gelfand et al, to treat hypertension, alead must be tunneled through the entire length of the patient's arm.Such a method is as invasive as, and suffers from most of the sameproblems as, the prior-described attempts at stimulation of the vitalparts of the central nervous system. In addition, the complicationsassociated with tunneling and removal of leads, which include infection,breakage, as well as the need to perform additional surgery, are nottrivial.

Yet others have described similar techniques for using electricaldevices, including external EA devices, for stimulating peripheralnerves and other body locations for treatment of various maladies. See,e.g., U.S. Pat. Nos. 4,535,784; 4,566,064; 5,195,517; 5,250,068;5,251,637; 5,891,181; 6,393,324; 6,006,134; 7,171,266; and 7,171,266.The methods and devices disclosed in these patents, however, typicallyutilize either large implantable stimulators having long leads that mustbe tunneled through tissue to reach the desired stimulation site, or useexternal devices that must interface with implanted electrodes viapercutaneous leads or wires passing through the skin. Such devices andmethods are still far too invasive, or are ineffective, and thus subjectto the same limitations and concerns, as are the previously describedelectrical stimulation devices.

From the above, it is seen that there is room for much improvement inthe electroacupuncture art for treating hypertension and other patientmaladies. In particular, it is seen that a much less invasive device andtechnique are needed for electroacupuncture stimulation of acupointsthat does not require the continual use of needles inserted through theskin, or long insulated lead wires, for the purpose of treatinghypertension.

SUMMARY

One characterization of the invention described herein is an ImplantableElectroAcupuncture Device (IEAD) that treats hypertension through theapplication of electroacupuncture (EA) stimulation pulses at a specifiedacupoint of a patient. The IEAD includes: (1) a small IEAD housinghaving an electrode configuration thereon that includes at least twoelectrodes, (2) pulse generation circuitry located within the IEADhousing that delivers EA stimulation pulses to the patient's body tissueat the specified acupoint, (3) a primary battery also located within theIEAD housing that provides the operating power for the IEAD to performits intended function, and (4) a sensor located within the IEAD housingthat is responsive to operating commands wirelessly communicated to theIEAD from a non-implanted location, these operating commands allowinglimited external control of the IEAD, such as ON/OFF and EA stimulationpulse amplitude adjustment.

In one preferred embodiment, the IEAD housing used as part of theinvention is coin-sized and -shaped, having a nominal diameter of 23 mm,and a thickness of only 2 to 3 mm.

One preferred embodiment provides a symmetrical electrode configurationon the housing of the IEAD. Such symmetrical electrode configurationincludes at least two electrodes, at least one of which is locatedsubstantially in the center of a first surface of the IEAD housing, andis referred to as a central electrode. The other electrode issymmetrically positioned around and at least 5 mm distant from thecenter of the central electrode, and is referred to as an annular orring electrode (or, in some instances, as a circumscribing electrode).This symmetry between the central electrode and the annular electrodeadvantageously focuses the electric field, and hence the EA stimulationcurrent created by application of an EA stimulation pulse to theelectrodes, deep into the tissue below the central electrode, where thedesired EA stimulation at the specified acupoint occurs. Hence, whenimplanted, the first surface of the IEAD housing is faced inwardly intothe patient's tissue below the acupoint, and a second surface of theIEAD housing, on the opposite side of the housing from the firstsurface, is faced outwardly to the patient's skin. One preferredembodiment of the IEAD housing uses one centrally located cathodeelectrode on the first surface of the IEAD housing, and one ring anodeelectrode located on a perimeter edge of a coin-sized and -shaped IEADhousing.

The pulse generation circuitry located within the IEAD housing iscoupled to the at least two electrodes. This pulse generation circuitryis configured to generate EA stimulation pulses in accordance with aspecified stimulation regimen. This stimulation regimen defines theduration and rate at which a stimulation session is applied to thepatient. The stimulation regimen requires that the stimulation sessionhave a duration of no more than T3 minutes and a rate of occurrence ofno more than once every T4 minutes. Advantageously, the duty cycle ofthe stimulation sessions, i.e., the ratio of T3/T4, is very low, nogreater than 0.05. A representative value for T3 is 30 minutes, and arepresentative value for T4 is 7 days. The individual EA stimulationpulses that occur within the stimulation session also have a duty cyclemeasured relative to the duration T3 of the stimulation session of nogreater than 5%. A representative pulse width and frequency for the EAstimulation pulses is 0.5 milliseconds, occurring at a pulse rate of 2Hz.

The primary battery contained within the IEAD housing and electricallycoupled to the pulse generation circuitry has a nominal output voltageof 3 volts, and an internal battery impedance that is at least 5 ohms,and may be as high as 150 ohms or more. Advantageously, electroniccircuitry within the IEAD housing controls the value of theinstantaneous surge current that may be drawn from the battery in orderto prevent any large drops in the battery output voltage. Avoiding largedrops in the battery output voltage assures that the circuits within theIEAD will continue to operate as designed without failure. Being able touse a primary battery that has a relatively high internal impedanceallows the battery to be thinner, and thus allows the device to bethinner and more easily implanted. The higher internal impedance alsoopens the door to using relatively inexpensive commercially-availabledisc batteries as the primary battery within the IEAD, thereby greatlyenhancing the manufacturability of the IEAD and significantly loweringits cost.

Another characterization of the invention described herein may bedescribed as a first method of treating hypertension in a patient usinga leadless, coin-sized implantable electroacupuncture device (IEAD).Such IEAD is powered by a small disc battery having a specified nominaloutput voltage of about 3.0 volts, and having an internal impedance ofat least 5 ohms.

The IEAD used to practice this first method is configured, usingelectronic circuitry within the IEAD, to generate EA stimulation pulsesin accordance with a specified stimulation regimen. The EA stimulationpulses generated in accordance with this stimulation regimen are appliedto the patient's tissue through at least two electrodes located on thehousing of the IEAD. These two electrodes include at least one centralelectrode, located in the center of a bottom surface of the coin-sizedhousing, and at least one annular electrode that surrounds the centralelectrode. The edge of the annular electrode closest to the centralelectrode is separated from the center of the central electrode by atleast 5 mm.

Using such an IEAD, the hypertension treatment method provided by thisfirst method includes the steps of: (a) implanting the IEAD below theskin surface of the patient at a selected acupoint; and (b) enabling theIEAD to provide stimulation pulses in accordance with a stimulationregimen.

To elaborate regarding the first step of the method, the selectedacupoint is preferably selected from the group of acupoints comprisingPC5 or PC6 (in the right or left forearm), and S36 or S37 (in the leftor right leg shin, just below the knee). When the IEAD is implanted, itis done so with its bottom surface (the “bottom” surface is that surfaceon which the central electrode is placed) facing into the patient'stissue below the patient's skin surface at the selected acupoint.

To elaborate regarding the second step of the method, the stimulationregimen provides a stimulation session at a rate of once every T4minutes, with each stimulation session having a duration of T3 minutes.The ratio of T3/T4 is no greater than 0.05. A preferred stimulationsession time T3 is 30 minutes, but T3 could be as short as 10 minutes oras long as 60 minutes. A preferred time between stimulation sessions T4is 7 days, but it could be as short as ½ day or as long as 10 days, orlonger, as needed to suit the needs of a particular patient.

Still further, the invention described herein may be characterized as asecond method for treating hypertension in a patient. This second methodcomprises the steps of: (a) implanting a coin-sized electroacupuncture(EA) device in the patient just below the patient's skin at a specifiedacupoint; (b) enabling the EA device to generate EA stimulation sessionsat a duty cycle that is less than 0.05, wherein each stimulation sessioncomprises a series of EA stimulation pulses; and (c) delivering the EAstimulation pulses of each stimulation session to the specified acupointthrough at least two electrodes attached to an outside surface of the EAdevice. The duty cycle is the ratio of T3/T4, where T3 is the durationin minutes of each stimulation session, and T4 is the time in minutesbetween stimulation sessions.

In a preferred application for this second method, the electrodesattached to the outside surface of the EA device are arranged in asymmetrical pattern. This symmetrical pattern of electrodesadvantageously concentrates, or focuses, the electric field emanatingfrom the electrode(s) downward into the tissue below the selectedacupoint to a location where the electroacupuncture stimulation is mosteffective. Another preferred application is for the electrodes to bealigned along the axis of two or more acupoints. For treatinghypertension, the specified acupoint at which the stimulation pulses areapplied is preferably selected from the group of acupoints thatincludes: PC5 and/or PC6 in the right or left forearm. For somepatients, the acupoints ST36 and/or ST37 in the left or right leg shin,just below the knee may also be added to the group.

Additionally, the invention described herein may be characterized as amethod of assembling an implantable electroacupuncture device (IEAD) ina round, thin, hermetically-sealed, coin-sized housing that electricallyand thermally isolates a feed-through pin assembly radially passingthrough a wall of the coin-sized housing from the high temperaturesassociated with welding the housing closed to hermetically seal itscontents. Such method of assembling includes the steps of:

-   -   a. forming a coin-sized housing having a bottom case and a top        cover plate, the top cover plate being adapted to fit over the        bottom case, the bottom case being substantially round and        having a diameter D2 that is nominally 23 mm and a perimeter        side wall extending all the way around the perimeter of the        bottom case, the perimeter side wall having a height W2, wherein        the ratio of W2 to D2 is no greater than about 0.13;    -   b. forming a recess in one segment of the side wall, the recess        extending radially inwardly from the side wall to a depth D3,        and the recess having an opening in a bottom wall portion        thereof;    -   c. hermetically sealing a feed-through assembly in the opening        in the bottom of the recess, the feed-through assembly having a        feed-through pin that passes through the opening without        contacting the edges of the opening, a distal end of the pin        extending radially outward beyond the side wall of the bottom        case, and a proximal end of the feed-through pin extending        radially inward toward the center of the bottom case, whereby        the feed-through pin assembly is hermetically bonded to the        opening in the side wall at a location in the bottom of the        recess that is a distance D3 from the perimeter side wall,        thereby thermally isolating the feed-through assembly from the        high temperatures that occur at the perimeter side wall when the        cover plate is welded to the edge of the perimeter side wall;    -   d. attaching a central electrode to the thin, coin-sized housing        at a central location on the bottom outside surface of the        feed-through housing;    -   e. inserting an electronic circuit assembly, including a        battery, inside of the bottom case, and connecting the proximal        end of the feed-though pin to an output terminal of the        electronic circuit assembly, and electrically connecting the        bottom case to a reference terminal of the battery;    -   f. baking out the assembly to remove moisture, back filling with        a mixture of He/Ar inert gas, and then welding the top cover        plate to the edges of the side wall of the bottom case, thereby        hermetically sealing the electronic circuit assembly, including        the battery, inside of the thin, coin-sized IEAD housing;    -   g. leak testing the welded assembly to assure a desired level of        hermeticity has been achieved;    -   h. placing an insulating layer of non-conductive material around        the perimeter edge of the thin coin-sized housing, then placing        a circumscribing electrode over the insulating layer of        non-conductive material, and then electrically connecting the        distal end of the feed-through pin to the circumscribing        electrode;    -   i. covering all external surface areas of the thin, coin-sized        housing with a layer of non-conductive material except for the        circumscribing electrode around the perimeter of the coin-sized        housing and the central electrode centrally located on the        bottom surface of the thin-coin-sized housing; and    -   j. performing electrical tests and visual inspections of the        IEAD to assure it meets all needed specifications.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and advantages of the inventionwill be more apparent from the following more particular descriptionthereof, presented in conjunction with the following drawings. Thesedrawings illustrate various embodiments of the principles describedherein and are part of the specification. The illustrated embodimentsare merely examples and do not limit the scope of the disclosure.

FIG. 1 is a perspective view of an Implantable Electroacupuncture Device(IEAD) made in accordance with the teachings presented herein.

FIG. 1A shows a view of a patient's limb (arm or leg) where an acupointhas been identified, and illustrates the manner used to implant an IEADat the selected acupoint.

FIG. 1B shows a sectional view of an IEAD implanted at a selectedacupoint, and illustrates the electric field gradient lines created whenan electroacupuncture (EA) pulse is applied to the tissue through thecentral electrode and ring electrode attached to the bottom surface andperimeter edge, respectively, of the IEAD housing.

FIG. 2 shows a plan view of the bottom surface of the IEAD housingillustrated in FIG. 1.

FIG. 2A shows a side view of the IEAD housing illustrated in FIG. 1.

FIG. 3 shows a plan view of one side, indicated as the “skin” side, ofthe IEAD housing or case illustrated in FIG. 1.

FIG. 3A is a sectional view of the IEAD of FIG. 3 taken along the lineA-A of FIG. 3.

FIG. 4 is a perspective view of the IEAD housing, including afeed-through pin, before the electronic components are placed therein,and before being sealed with a “skin side” cover plate.

FIG. 4A is a side view of the IEAD housing of FIG. 4.

FIG. 5 is a plan view of the empty IEAD housing shown in FIG. 4.

FIG. 5A depicts a sectional view of the IEAD housing of FIG. 5 takenalong the section line A-A of FIG. 5.

FIG. 5B shows an enlarged view or detail of the portion of FIG. 5A thatis encircled with the line B.

FIG. 6 is a perspective view of an electronic assembly, including abattery, that is adapted to fit inside of the empty housing of FIG. 4and FIG. 5.

FIGS. 6A and 6B show a plan view and side view, respectively, of theelectronic assembly shown in FIG. 6.

FIG. 7 is an exploded view of the IEAD assembly, illustrating itsconstituent parts.

FIG. 7A schematically illustrates a few alternative electrodeconfigurations that may be used with the invention.

FIG. 8A illustrates a functional block diagram of the electroniccircuits used within an IEAD of the type described herein.

FIG. 8B shows a basic boost converter circuit configuration, and is usedto model how the impedance of the battery R_(BAT) can affect itsperformance.

FIG. 9A illustrates a typical voltage and current waveform for thecircuit of FIG. 8 when the battery impedance R_(BAT) is small.

FIG. 9B shows the voltage and current waveform for the circuit of FIG.8B when the battery impedance R_(BAT) is large.

FIG. 10 shows one preferred boost converter circuit and a functionalpulse generation circuit configuration for use within the IEAD.

FIG. 11 shows an alternate boost converter circuit configuration and afunctional pulse generation circuit for use within the IEAD.

FIG. 12 shows a refinement of the circuit configuration of FIG. 11.

FIG. 13A shows one preferred schematic configuration for an implantableelectroacupuncture device (IEAD) that utilizes the boost converterconfiguration shown in FIG. 10.

FIG. 13B shows current and voltage waveforms associated with theoperation of the circuit shown in FIG. 13A.

FIG. 14 shows another preferred schematic configuration for an IEADsimilar to that shown in FIG. 13A, but which uses an alternate outputcircuitry configuration for generating the stimulus pulses.

FIG. 15A shows a timing waveform diagram of representative EAstimulation pulses generated by the IEAD device during a stimulationsession.

FIG. 15B shows a timing waveform diagram of multiple stimulationsessions, and illustrates the waveforms on a more condensed time scale.

FIG. 16 shows a state diagram that shows the various states in which theIEAD may be placed through the use of an external magnet.

Appendix A, submitted with one or more of Applicant's parentapplications, illustrates some examples of alternate symmetricalelectrode configurations that may be used with an IEAD of the typedescribed herein.

Appendix B, also submitted with one or more of Applicant's parentapplications, illustrates a few examples of non-symmetrical electrodeconfigurations that may be used with an IEAD made in accordance with theteachings herein.

Appendix C, also submitted with one or more of Applicant's parentapplications, shows an example of the code used in the micro-controllerIC (e.g., U2 in FIG. 14) to control the basic operation and programmingof the IEAD, e.g., to Turn the IEAD ON/OFF, adjust the amplitude of thestimulus pulse, and the like, using only an external magnet as anexternal communication element.

Appendix D, also submitted with one or more of Applicant's parentapplications, contains selected pages from the WHO Standard AcupuncturePoint Locations 2008 reference book.

Appendices A, B, C and D are incorporated by reference herein, andcomprise a part of the specification of this patent application.

Throughout the drawings and appendices, identical reference numbersdesignate similar, but not necessarily identical, elements.

DETAILED DESCRIPTION Overview

Disclosed herein is an implantable, coin-shaped, self-contained,symmetrical, leadless electroacupuncture (EA) device having at least twoelectrode contacts mounted on the surface of its housing. In onepreferred embodiment, the electrodes include a central cathode electrodeon a bottom side of the housing, and an annular anode electrode thatsurrounds the cathode. In another preferred embodiment, the anodeannular electrode is a ring electrode placed around the perimeter edgeof the coin-shaped housing.

The EA device is leadless. This means there are no leads or electrodesat the distal end of leads (common with most implantable electricalstimulators) that have to be positioned and anchored at a desiredstimulation site. Also, because there are no leads, no tunneling throughbody tissue or blood vessels is required in order to provide a path forthe leads to return and be connected to a tissue stimulator (also commonwith most electrical stimulators).

The EA device is adapted to be implanted through a very small incision,e.g., less than 2-3 cm in length, directly adjacent to a selectedacupuncture site (“acupoint”) known to moderate or affect a hypertensioncondition of a patient.

The EA device is easy to implant. Also, most embodiments aresymmetrical. This means that there is no way that it can be implantedincorrectly (unless the physician puts it in up-side-down, which wouldbe difficult to do given the markings on its case). All that need bedone is to cut the incision, and slide the device in place through theincision. Once the implant pocket has been prepared, it is as easy assliding a coin into a slot. Such implantation can usually be completedin less than 10 minutes in an outpatient setting, or in a doctor'soffice. Only minor, local anesthesia need be used. No major orsignificant complications are envisioned for the implant procedure. TheEA device can also be easily and quickly explanted, if needed.

The EA device is self-contained. It includes a primary battery toprovide its operating power. It includes all of the circuitry it needs,in addition to the battery, to allow it to perform its intended functionfor several years. Once implanted, the patient will not even know it isthere, except for a slight tingling that may be felt when the device isdelivering stimulus pulses during a stimulation session. Also, onceimplanted, the patient can just forget about it. There are nocomplicated user instructions that must be followed. Just turn it on. Nomaintenance is needed. Moreover, should the patient want to disable theEA device, i.e., turn it OFF, or change stimulus intensity, he or shecan do so using, e.g., an external magnet.

The EA device can operate for several years because it is designed to bevery efficient. Stimulation pulses applied by the EA device at aselected acupoint through its electrodes formed on its case are appliedat a very low duty cycle in accordance with a specified stimulationregimen. The stimulation regimen applies EA stimulation during astimulation session that lasts at least 10 minutes, typically 30minutes, and rarely longer than 60 minutes. These stimulation sessions,however, occur at a very low duty cycle. In one preferred treatmentregimen, for example, a stimulation session having a duration of 30minutes is applied to the patient just once a week. The stimulationregimen, and the selected acupoint at which the stimulation is applied,are designed and selected to provide efficient and effective EAstimulation for the treatment of the patient's hypertension condition.

The EA device is, compared to most implantable medical devices,relatively easy to manufacture and uses few components. This not onlyenhances the reliability of the device, but helps keep the manufacturingcosts low, which in turn allows the device to be more affordable to thepatient. One key feature included in the mechanical design of the EAdevice is the use of a radial feed-through assembly to connect theelectrical circuitry inside of its housing to one of the electrodes onthe outside of the housing. The design of this radial feed-through pinassembly greatly simplifies the manufacturing process. The processplaces the temperature sensitive hermetic bonds used in the assembly—thebond between a pin and an insulator and the bond between the insulatorand the case wall—away from the perimeter of the housing as the housingis hermetically sealed at the perimeter with a high temperature laserwelding process, thus preserving the integrity of the hermetic bondsthat are part of the feed-through assembly.

In operation, the EA device is safe to use. There are no horrificfailure modes that could occur. Because it operates at a very low dutycycle (i.e., it is OFF much, much more than it is ON), it generateslittle heat. Even when ON, the amount of heat it generates is not much,less than 1 mW, and is readily dissipated. Should a component or circuitinside of the EA device fail, the device will simply stop working. Ifneeded, the EA device can then be easily explanted.

Another key feature included in the design of the EA device is the useof a commercially-available battery as its primary power source. Small,thin, disc-shaped batteries, also known as “coin cells,” are quitecommon and readily available for use with most modern electronicdevices. Such batteries come in many sizes, and use variousconfigurations and materials. However, insofar as applicants are aware,such batteries have never been used in implantable medical devicespreviously. This is because their internal impedance is, or has alwaysthought to have been, much too high for such batteries to be ofpractical use within an implantable medical device where powerconsumption must be carefully monitored and managed so that the device'sbattery will last as long as possible, and so that dips in the batteryoutput voltage (caused by any sudden surge in instantaneous batterycurrent) do not occur that could compromise the performance of thedevice. Furthermore, the energy requirements of other active implantabletherapies are far greater than can be provided by such coin cellswithout frequent replacement.

The EA device disclosed herein advantageously employs power-monitoringand power-managing circuits that prevent any sudden surges in batteryinstantaneous current, or the resulting drops in battery output voltage,from ever occurring, thereby allowing a whole family ofcommercially-available, very thin, high-output-impedance, relatively lowcapacity, small disc batteries (or “coin cells”) to be used as the EAdevice's primary battery without compromising the EA device'sperformance. As a result, instead of specifying that the EA device'sbattery must have a high capacity, e.g., greater than 200 mAh, with aninternal impedance of, e.g., less than 5 ohms, which would eitherrequire a thicker battery and/or preclude the use ofcommercially-available coin-cell batteries, the EA device of the presentinvention can readily employ a battery having a relatively low capacity,e.g., less than 60 mAh, and a high battery impedance, e.g., greater than5 ohms.

Moreover, the power-monitoring, power-managing, as well as the pulsegeneration, and control circuits used within the EA device arerelatively simple in design, and may be readily fashioned fromcommercially-available integrated circuits (IC's) orapplication-specific integrated circuits (ASIC's), supplemented withdiscrete components, as needed. In other words, the electronic circuitsemployed within the EA device need not be complex nor expensive, but aresimple and inexpensive, thereby making it easier to manufacture the EAdevice and to provide it to patients at an affordable cost.

Definitions

As used herein, “annular”, “circumferential”, “circumscribing”,“surrounding” or similar terms used to describe an electrode orelectrode array, or electrodes or electrode arrays, (where the phrase“electrode or electrode array,” or “electrodes or electrode arrays,” isalso referred to herein as “electrode/array,” or “electrodes/arrays,”respectively) refers to an electrode/array shape or configuration thatsurrounds or encompasses a point or object, such as another electrode,without limiting the shape of the electrode/array or electrodes/arraysto be circular or round. In other words, an “annular” electrode/array(or a “circumferential” electrode/array, or a “circumscribing”electrode/array, or a “surrounding” electrode/array), as used herein,may be many shapes, such as oval, polygonal, starry, wavy, and the like,including round or circular.

“Nominal” or “about” when used with a mechanical dimension, e.g., anominal diameter of 23 mm, means that there is a tolerance associatedwith that dimension of no more than plus or minus (+/−) 5%. Thus, adimension that is nominally 23 mm means a dimension of 23 mm+/−(0.05×23mm=1.15 mm).

“Nominal” when used to specify a battery voltage is the voltage by whichthe battery is specified and sold. It is the voltage you expect to getfrom the battery under typical conditions, and it is based on thebattery cell's chemistry. Most fresh batteries will produce a voltageslightly more than their nominal voltage. For example, a new nominal 3volt lithium coin-sized battery will measure more than 3.0 volts, e.g.,up to 3.6 volts under the right conditions. Since temperature affectschemical reactions, a fresh warm battery will have a greater maximumvoltage than a cold one. For example, as used herein, a “nominal 3 volt”battery voltage is a voltage that may be as high as 3.6 volts when thebattery is brand new, but is typically between 2.7 volts and 3.4 volts,depending upon the load applied to the battery (i.e., how much currentis being drawn from the battery) when the measurement is made and howlong the battery has been in use.

Mechanical Design

Turning first to FIG. 1, there is shown a perspective view of onepreferred embodiment of an implantable electroacupuncture device (IEAD)100 made in accordance with the teachings disclosed herein. The IEAD 100may also sometimes be referred to as an implantable electroacupuncturestimulator (IEAS). As seen in FIG. 1, the IEAD 100 has the appearance ofa disc or coin, having a top side 102, a bottom side 106 and an edgeside 104.

As used herein, the “top” side of the IEAD 100 is the side that ispositioned closest to the skin of the patient when the IEAD isimplanted. The “bottom” side is the side of the IEAD that is farthestaway from the skin when the IEAD is implanted. The “edge” of the IEAD isthe side that connects or joins the top side to the bottom side. In FIG.1, the IEAD 100 is oriented to show the bottom side 106 and a portion ofthe edge side 104.

Many of the features associated with the mechanical design of the IEAD100 shown in FIG. 1 are the subject of a prior U.S. Provisional PatentApplication, entitled “Radial Feed-Through Packaging for An ImplantableElectroacupuncture Device”, Application No. 61/676,275, filed 26 Jul.2012, which application is incorporated here by reference.

It should be noted here that throughout this application, the terms IEAD100, IEAD housing 100, bottom case 124, can 124, or IEAD case 124, orsimilar terms, are used interchangeably to mean the same thing. Thecontext should dictate what is meant by these terms when usedinterchangeably. As the drawings illustrate, particularly FIG. 7, thereis a bottom case 124 that comprises the “can” or “container” wherein thecomponents of the IEAD 100 are first placed and assembled duringmanufacture of the IEAD 100. When all of the components are assembledand placed within the bottom case 124, a top plate 122 is welded to thebottom case 124 to form the hermetically-sealed housing of the IEAD. Thecathode electrode 110 is attached to the outside of the bottom case 124,and the ring anode electrode 120 is attached, along with its insulatinglayer 129, around the perimeter edge 104 of the bottom case 124.Finally, a layer of silicone molding 125 covers the IEAD housing exceptfor the outside surfaces of the anode ring electrode and the cathodeelectrode.

The embodiment of the IEAD 100 shown in FIG. 1 utilizes two electrodes,a cathode electrode 110 that is centrally positioned on the bottom side106 of the IEAD 100, and an anode electrode 120. The anode electrode 120is a ring electrode that fits around the perimeter edge 104 of the IEAD100. Not visible in FIG. 1, but which is described hereinafter inconnection with the description of FIG. 7, is a layer of insulatingmaterial 129 that electrically insulates the anode ring electrode 120from the perimeter edge 104 of the housing or case 124.

Not visible in FIG. 1, but a key feature of the mechanical design of theIEAD 100, is the manner in which an electrical connection is establishedbetween the ring electrode 120 and electronic circuitry carried insideof the IEAD 100. This electrical connection is established using aradial feed-through pin that fits within a recess formed in a segment ofthe edge of the case 124, as explained more fully below in connectionwith the description of FIGS. 5, 5A, 5B and 7.

In contrast to the feed-through pin that establishes electrical contactwith the anode electrode, electrical connection with the cathodeelectrode 110 is established simply by forming or attaching the cathodeelectrode 110 to the bottom 106 of the IEAD case 124. In order toprevent the entire case 124 from functioning as the cathode (which isdone to better control the electric fields established between the anodeand cathode electrodes), the entire IEAD housing is covered in a layerof silicone molding 125 (see FIG. 7), except for the outside surface ofthe anode ring electrode 120 and the cathode electrode 110.

The advantage of using a central cathode electrode and a ring anodeelectrode is described in U.S. Provisional Patent Application No.61/672,257, filed 6 Mar. 2012, entitled “Electrode Configuration forImplantable Electroacupuncture Device”, which application isincorporated herein by reference. One significant advantage of thiselectrode configuration is that it is symmetrical. That is, whenimplanted, the surgeon or other medical personnel performing the implantprocedure, need only assure that the cathode side of the IEAD 100 isfacing down, i.e., facing deeper into the tissue, and that the IEAD isover the desired acupoint, or other tissue location, that is intended toreceive the electroacupuncture (EA) stimulation. The orientation of theIEAD 100 is otherwise not important.

Implantation of the IEAD is illustrated in FIG. 1A. Shown in FIG. 1A isa limb 80 of the patient wherein an acupoint 90 has been identified thatis to receive acupuncture treatment (in this case electroacupuncturetreatment). An incision 82 is made into the limb 80 a short distance,e.g., 10-15 mm, away from the acupoint 90. A slot 84 (parallel to thearm) is formed at the incision by lifting the skin closest to theacupoint up at the incision. As necessary, the surgeon may form a pocketunder the skin at the acupoint location. The IEAD 100, with its top side102 being closest to the skin, is then slid through the slot 84 into thepocket so that the center of the IEAD is located under the acupoint 90.This implantation process is as easy as inserting a coin into a slot.With the IEAD 100 in place, the incision is sewn or otherwise closed,leaving the IEAD 100 under the skin 80 at the location of the acupoint90 where electroacupuncture (EA) stimulation is desired.

It should be noted that while FIG. 1B illustrates the acupoint 90 asbeing on the surface of the skin, the actual location where acupuncturetreatment (whether it be administered through a needle, or throughelectroacupuncture (EA) stimulation) is most effective for purposes ofthe present invention is at a distance d2 below the skin surface alongan axis line 92 extending orthogonally into the skin from the locationon the skin where the acupoint 90 is indicated as being positioned. Thedistance d2 varies depending upon where the acupoint is located on thebody. The depth d2 where EA stimulation is most effective for purposesof the present invention (to treat hypertension) appears to be betweenabout 6 to 10 mm below the skin surface in the location of an acupoint90 located in the forearm (e.g., acupoints PC5 and/or PC6); and may bemuch deeper, e.g., 1 to 2 cm, in the location of an acupoint 90 locatedin the leg (e.g., acupoints ST36 and/or ST37).

FIG. 1B shows a sectional view of the IEAD 100 implanted so as to becentrally located under the skin at the selected acupoint 90, and overthe acupoint axis line 92. Usually, for most patients, the IEAD 100 isimplanted at a depth d1 of approximately 2-4 mm under the skin. The topside 102 of the IEAD is nearest to the skin 80 of the patient. Thebottom side 106 of the IEAD, which is the side on which the centralcathode electrode 110 resides, is farthest from the skin. Because thecathode electrode 110 is centered on the bottom of the IEAD, and becausethe IEAD 100 is implanted so as to be centered under the location on theskin where the acupoint 90 is located, the cathode 110 is also centeredover the acupoint axis line 92.

FIG. 1B further illustrates the electric field gradient lines 88 thatare created in the body tissue 86 surrounding the acupoint 90 and theacupoint axis line 92. (Note: for purposes herein, when reference ismade to providing EA stimulation at a specified acupoint, it isunderstood that the EA stimulation is provided at a depth ofapproximately d2 below the location on the skin surface where theacupoint is indicated as being located.) As seen in FIG. 1B, theelectric field gradient lines are strongest along a line that coincideswith, or is near to, the acupoint axis line 92. It is thus seen that oneof the main advantages of using a symmetrical electrode configurationthat includes a centrally located electrode surrounded by an annularelectrode is that the precise orientation of the IEAD within its implantlocation is not important. So long as one electrode is centered over thedesired target location, and the other electrode surrounds the firstelectrode (e.g., as an annular electrode), a strong electric fieldgradient is created that is aligned with the acupoint axis line. Thiscauses the EA stimulation current to flow along (or very near) theacupoint axis line 92, and will result in the desired EA stimulation inthe tissue at a depth d2 below the acupoint location indicated on theskin.

FIG. 2 shows a plan view of the “cathode” side (or the bottom side) ofthe IEAD 100. As seen in FIG. 2, the cathode electrode 110 appears as acircular electrode, centered on the cathode side, having a diameter D1.The IEAD housing has a diameter D2 and an overall thickness or width W2.For the preferred embodiment shown in these figures, D1 is about 4 mm,D2 is about 23 mm and W2 is a little over 2 mm (2.2 mm).

FIG. 2A shows a side view of the IEAD 100. The ring anode electrode 120,best seen in FIG. 2A, has a width W1 of about 1.0 mm, or approximately ½of the width W2 of the IEAD.

FIG. 3 shows a plan view of the “skin” side (the top side) of the IEAD100. As will be evident from subsequent figure descriptions, e.g., FIGS.5A and 5B, the skin side of the IEAD 100 comprises a top plate 122 thatis welded in place once the bottom case 124 has all of the electroniccircuitry, and other components, placed inside of the housing.

FIG. 3A is a sectional view of the IEAD 100 of FIG. 1 taken along theline A-A of FIG. 3. Visible in this sectional view is the feed-throughpin 130, including the distal end of the feed-through pin 130 attachedto the ring anode electrode 120. Also visible in this section view is anelectronic assembly 133 on which various electronic components aremounted, including a disc-shaped battery 132. FIG. 3A furtherillustrates how the top plate 122 is welded, or otherwise bonded, to thebottom case 124 in order to form the hermetically-sealed IEAD housing100. (Note, in FIG. 3A, the “top” plate 122 is actually shown on theleft side of the “bottom” case 124, which is shown on the right side.This is because the orientation of the drawing in FIG. 3A shows the IEAD100 standing on its edge.)

FIG. 4 shows a perspective view of the IEAD case 124, including thefeed-through pin 130, before the electronic components are placedtherein, and before being sealed with the “skin side” cover plate 122.The case 124 is similar to a shallow “can” without a lid, having a shortside wall around its perimeter. Alternatively, the case 124 may beviewed as a short cylinder, closed at one end but open at the other.(Note, in the medical device industry the housing of an implanted deviceis often referred to as a “can”.) The feed-through pin 130 passesthrough a segment of the wall of the case 124 that is at the bottom of arecess 140 formed in the wall. The use of this recess 140 to hold thefeed-through pin 130 is a key feature of the invention because it keepsthe temperature-sensitive portions of the feed-through assembly (thoseportions that could be damaged by excessive heat) away from the thermalshock and residual weld stress inflicted upon the case 124 when thecover plate 122 is welded thereto.

FIG. 4A is a side view of the IEAD case 124, and shows an annular rim126 formed on both sides of the case 124. The ring anode electrode 120fits between these rims 126 once the ring electrode 120 is positionedaround the edge of the case 124. A silicone insulator layer 129 (seeFIG. 7) is placed between the backside of the ring anode electrode 120and the perimeter edge of the case 124 when the ring anode electrode 120is placed around the edge of the case 124.

FIG. 5 shows a plan view of the empty IEAD case 124 shown in theperspective view of FIG. 4. An outline of the recess cavity 140 is alsoseen in FIG. 5, as is the feed-through pin 130. A bottom edge of therecess cavity 140 is located a distance D5 radially inward from the edgeof the case 124. In one embodiment, the distance D5 is between about 2.0to 2.5 mm. The feed-through pin 130, which is just a piece of solidwire, is shown in FIG. 5 extending radially outward from the case 124above the recess cavity 140 and radially inward from the recess cavitytowards the center of the case 124. The length of this feed-through pin130 is trimmed, as needed, when a distal end (extending above therecess) is connected (welded) to the anode ring electrode 120 (passingthrough a hole in the ring electrode 120 prior to welding) and when aproximal end of the feed-through pin 130 is connected to an outputterminal of the electronic assembly 133.

FIG. 5A depicts a sectional view of the IEAD housing 124 of FIG. 5 takenalong the section line A-A of FIG. 5. FIG. 5B shows an enlarged view ordetail of the portion of FIG. 5A that is encircled with the line B.Referring to FIGS. 5A and 5B jointly, it is seen that the feed-throughpin 130 is embedded within an insulator material 136, which insulatingmaterial 136 has a diameter of D3. The feed-through pin assembly (whichpin assembly comprises the combination of the pin 130 embedded into theinsulator material 136) resides on a shoulder around an opening or holeformed in the bottom of the recess 140 having a diameter D4. For theembodiment shown in FIGS. 5A and 5B, the diameter D3 is 0.95-0.7 mm,where the −0.7 mm is a tolerance. (Thus, with the tolerance considered,the diameter D3 may range from 0.88 mm to 0.95 mm) The diameter D4 is0.80 mm with a tolerance of −0.6 mm. (Thus, with the toleranceconsidered, the diameter D4 could range from 0.74 mm to 0.80 mm).

The feed-through pin 130 is preferably made of pure platinum 99.95%. Apreferred material for the insulator material 136 is Ruby or alumina.The IEAD case 124, and the cover 122, are preferably made from titanium.The feed-through assembly, including the feed-through pin 130,ruby/alumina insulator 136 and the case 124 are hermetically sealed as aunit by gold brazing. Alternatively, active metal brazing can be used.(Active metal brazing is a form of brazing which allows metal to bejoined to ceramic without metallization.)

The hermeticity of the sealed IEAD housing is tested using a helium leaktest, as is common in the medical device industry. The helium leak rateshould not exceed 1×10⁻⁹ STD cc/sec at 1 atm pressure. Other tests areperformed to verify the case-to-pin resistance (which should be at least15×10⁶ Ohms at 100 volts DC), the avoidance of dielectric breakdown orflashover between the pin and the case 124 at 400 volts AC RMS at 60 Hzand thermal shock.

One important advantage provided by the feed-through assembly shown inFIGS. 4A, 5, 5A and 5B is that the feed-through assembly made from thefeed-through pin 130, the ruby insulator 136 and the recess cavity 140(formed in the case material 124) may be fabricated and assembled beforeany other components of the IEAD 100 are placed inside of the IEAD case124. This advantage greatly facilitates the manufacture of the IEADdevice.

Turning next to FIG. 6, there is shown a perspective view of anelectronic assembly 133. The electronic assembly 133 includes amulti-layer printed circuit (pc) board 138, or equivalent mountingstructure, on which a battery 132 and various electronic components 134are mounted. This assembly is adapted to fit inside of the empty bottomhousing 124 of FIG. 4 and FIG. 5.

FIGS. 6A and 6B show a plan view and side view, respectively, of theelectronic assembly 133 shown in FIG. 6. The electronic components areassembled and connected together so as to perform the circuit functionsneeded for the IEAD 100 to perform its intended functions. These circuitfunctions are explained in more detail below under the sub-heading“Electrical Design”. Additional details associated with these functionsmay also be found in many of the patent applications referenced above.

FIG. 7 shows an exploded view of the complete IEAD 100, illustrating itsmain constituent parts. As seen in FIG. 7, the IEAD 100 includes,starting on the right and going left, a cathode electrode 110, a ringanode electrode 120, an insulating layer 129, the bottom case 124 (the“can” portion of the IEAD housing, and which includes the feed-throughpin 130 which passes through an opening in the bottom of the recess 140formed as part of the case, but wherein the feed-through pin 130 isinsulated and does not make electrical contact with the metal case 124by the ruby insulator 136), the electronic assembly 133 (which includesthe battery 132 and various electronic components 134 mounted on a pcboard 138) and the cover plate 122. The cover plate 122 is welded to theedge of the bottom case 124 using laser beam welding, or some equivalentprocess, as one of the final steps in the assembly process.

Other components included in the IEAD assembly, but not necessarilyshown or identified in FIG. 7, include adhesive patches for bonding thebattery 132 to the pc board 138 of the electronic assembly 133, and forbonding the electronic assembly 133 to the inside of the bottom of thecase 124. To prevent high temperature exposure of the battery 132 duringthe assembly process, conductive epoxy is used to connect a batteryterminal to the pc board 138. Because the curing temperature ofconductive epoxy is 125° C., the following process is used: (a) firstcure the conductive epoxy of a battery terminal ribbon to the pc boardwithout the battery, (b) then glue the battery to the pc board usingroom temperature cure silicone, and (c) laser tack weld the connectingribbon to the battery.

Also not shown in FIG. 7 is the manner of connecting the proximal end ofthe feed-through pin 130 to the pc board 138, and connecting a pc boardground pad to the case 124. A preferred method of making theseconnections is to use conductive epoxy and conductive ribbons, althoughother connection methods known in the art may also be used.

Further shown in FIG. 7 is a layer of silicon molding 125 that is usedto cover all surfaces of the entire IEAD 100 except for the anode ringelectrode 120 and the circular cathode electrode 110. An overmodlingprocess is used to accomplish this, although overmolding using siliconeLSR 70 (curing temperature of 120° C.) with an injection moldlingprocess cannot be used. Overmolding processes that may be used include:(a) molding a silicone jacket and gluing the jacket onto the case usingroom temperature cure silicone (RTV) inside of a mold, and curing atroom temperature; (b) injecting room temperature cure silicone in a PEEKor Teflon® mold (silicone will not stick to the Teflon® or PEEKmaterial); or (c) dip coating the IEAD 100 in room temperature curesilicone while masking the electrode surfaces that are not to be coated.(Note: PEEK is a well known semicrystalline thermoplastic with excellentmechanical and chemical resistance properties that are retained to hightemperatures.)

When assembled, the insulating layer 129 is positioned underneath thering anode electrode 120 so that the anode electrode does not short tothe case 124. The only electrical connection made to the anode electrode120 is through the distal tip of the feed-through pin 130. Theelectrical contact with the cathode electrode 110 is made through thecase 124. However, because the entire IEAD is coated with a layer ofsilicone molding 125, except for the anode ring electrode 120 and thecircular cathode electrode 110, all stimulation current generated by theIEAD 100 must flow between the exposed surfaces of the anode andcathode.

It is noted that while the preferred configuration described herein usesa ring anode electrode 120 placed around the edges of the IEAD housing,and a circular cathode electrode 110 placed in the center of the cathodeside of the IEAD case 124, such an arrangement could be reversed, i.e.,the ring electrode could be the cathode, and the circular electrodecould be the anode.

Moreover, the location and shape of the electrodes may be configureddifferently than is shown in the one preferred embodiment describedabove in connection with FIGS. 1, and 2-7. For example, the ring anodeelectrode 120 need not be placed around the perimeter of the device, butsuch electrode may be a flat circumferential electrode that assumesdifferent shapes (e.g., round or oval) that is placed on the bottom oron the top surface of the IEAD so as to surround the central electrode.Further, for some embodiments, the surfaces of the anode and cathodeelectrodes may have convex surfaces.

It is also noted that while one preferred embodiment has been disclosedherein that incorporates a round, or short cylindrical-shaped housing,also referred to as a coin-shaped housing, the invention does notrequire that the case 124 (which may also be referred to as a“container”), and its associated cover plate 122, be round. The casecould just as easily be an oval-shaped, rectangular-shaped (e.g., squarewith smooth corners), polygonal-shaped (e.g., hexagon-, octagon-,pentagon-shaped), button-shaped (with convex top or bottom for asmoother profile) device. Any of these alternate shapes, or others,would still permit the basic principles of the invention to be used tohelp protect a feed-through assembly from being exposed to excessiveheat during assembly, and to allow the thin device to provide thebenefits described herein related to its manufacture, implantation anduse. For example, as long as the device remains relatively thin, e.g.,no more than about 2-3 mm, and does not have a maximum linear dimensiongreater than about 25 mm, then the device can be easily implanted in apocket over the tissue area where the selected acupoint(s) is located.As long as there is a recess in the wall around the perimeter of thecase wherein the feed-through assembly may be mounted, which recesseffectively moves the wall or edge of the case inwardly into the housinga safe thermal distance, as well as a safe residual weld stressdistance, from the perimeter wall where a hermetically-sealed weldoccurs, the principles of the invention apply.

Further, it should be noted that while the preferred configuration ofthe IEAD described herein utilizes a central electrode on one of itssurfaces that is round, having a diameter of nominally 4 mm, suchcentral electrode need not necessarily be round. It could be ovalshaped, polygonal-shaped, or shaped otherwise, in which case its size isbest defined by its maximum width, which will generally be no greaterthan about 7 mm.

Finally, it is noted that the electrode arrangement may be modifiedsomewhat, and the desired attributes of the invention may still beachieved. For example, as indicated previously, one preferred electrodeconfiguration for use with the invention utilizes a symmetricalelectrode configuration, e.g., an annular electrode of a first polaritythat surrounds a central electrode of a second polarity. Such asymmetrical electrode configuration makes the implantableelectroacupuncture device (IEAD) relatively immune to being implanted inan improper orientation relative to the body tissue at the selectedacupoint(s) that is being stimulated. However, an electrodeconfiguration that is not symmetrical may still be used and many of thetherapeutic effects of the invention may still be achieved. For example,two spaced-apart electrodes on a bottom surface of the housing, one of afirst polarity, and a second of a second polarity, could still, whenoriented properly with respect to a selected acupoint tissue location,provide some desired therapeutic results

FIG. 7A schematically illustrates a few alternative electrodeconfigurations that may be used with the invention. The electrodeconfiguration schematically shown in the upper left corner of FIG. 7A,identified as “I”, schematically illustrates one central electrode 110surrounded by a single ring electrode 120. This is one of the preferredelectrode configurations that has been described previously inconnection, e.g., with the description of FIGS. 1, 1A, 1B and 7, and ispresented in FIG. 7A for reference and comparative purposes.

In the lower left corner of FIG. 7A, identified as “II”, anelectrode/array configuration is schematically illustrated that has acentral electrode 310 of a first polarity surrounded by an electrodearray 320 a of two electrodes of a second polarity. When the twoelectrodes (of the same polarity) in the electrode array 320 a areproperly aligned with the body tissue being stimulated, e.g., alignedwith the longitudinal axis of the limb 80 (see FIG. 1A) wherein the IEADis implanted, then such electrode configuration can stimulate the bodytissue at or near the desired acupoint(s) with the same, or almost thesame, efficacy as can the electrode configuration I (upper right cornerof FIG. 7A).

Note, as has already been described above, the phrase “electrode orelectrode array,” or “electrodes or electrode arrays,” may also bereferred to herein as “electrode/array” or “electrodes/arrays,”respectively. For the ease of explanation, when an electrode array isreferred to herein that comprises a plurality (two or more) ofindividual electrodes of the same polarity, the individual electrodes ofthe same polarity within the electrode array may also be referred to as“individual electrodes”, “segments” of the electrode array, “electrodesegments”, or just “segments”.

In the lower right corner of FIG. 7A, identified as “III”, en electrodeconfiguration is schematically illustrated that has a centralelectrode/array 310 b of three electrode segments of a first polaritysurrounded by an electrode array 320 b of three electrode segments of asecond polarity. As shown in FIG. 7A-III, the three electrode segmentsof the electrode array 320 b are symmetrically positioned within thearray 320 b, meaning that they are positioned more or less equidistantfrom each other. However, a symmetrical positioning of the electrodesegments within the array is not necessary to stimulate the body tissueat the desired acupoint(s) with some efficacy.

In the upper right corner of FIG. 7A, identified as “IV”, anelectrode/array configuration is schematically illustrated that has acentral electrode array 310 c of a first polarity surrounded by anelectrode array 320 c of four electrode segments of a second polarity.The four electrode segments of the electrode array 320 c are arrangedsymmetrically in a round or oval-shaped array. The four electrodesegments of the electrode array 310 b are likewise arrangedsymmetrically in a round or oval-shaped array. Again, however, whilepreferred for many configurations, the use of a symmetricalelectrode/array, whether as a central electrode array 310 or as asurrounding electrode/array 320, is not required in all configurations.

The electrode configurations I, II, III and IV shown schematically inFIG. 7A are only representative of a few electrode configurations thatmay be used with the present invention. Further, it is to be noted thatthe central electrode/array 310 need not have the same number ofelectrode segments as does the surrounding electrode/array 320.Typically, the central electrode/array 310 of a first polarity will be asingle electrode; whereas the surrounding electrode/array 320 of asecond polarity may have n individual electrode segments, where n is aninteger that can vary from 1, 2, 3, . . . n. Thus, for a circumferentialelectrode array where n=4, there are four electrode segments of the samepolarity arranged in circumferential pattern around a centralelectrode/array. If the circumferential electrode array with n=4 is asymmetrical electrode array, then the four electrode segments will bespaced apart equally in a circumferential pattern around a centralelectrode/array. When n=1, the circumferential electrode array reducesto a single circumferential segment or a single annular electrode thatsurrounds a central electrode/array.

Additionally, the polarities of the electrode/arrays may be selected asneeded. That is, while the central electrode/array 310 is typically acathode (−), and the surrounding electrode/array 320 is typically ananode (+), these polarities may be reversed.

It should be noted that the shape of the circumferentialelectrode/array, whether circular, oval, or other shape, need notnecessarily be the same shape as the IEAD housing, unless thecircumferential electrode/array is attached to a perimeter edge of theIEAD housing. The IEAD housing may be round, or it may be oval, or itmay have a polygon shape, or other shape, as needed to suit the needs ofa particular manufacturer and/or patient.

Additional electrode configurations, both symmetrical electrodeconfigurations and non-symmetrical electrode configurations, that may beused with an EA stimulation device as described herein, are described inAppendices A and B of Applicant's parent application, application Ser.No. 13/598,575, incorporated herein by reference.

Electrical Design

Next, with reference to FIGS. 8A-14, the electrical design and operationof the circuits employed within the IEAD 100 will be described. Moredetails associated with the design of the electrical circuits describedherein may be found in the following previously-filed U.S. ProvisionalPatent Applications, which applications are incorporated herein byreference: (1) Appl. No. 61/575,869, filed Aug. 30, 2012, entitledImplantable Electroacupuncture Device and Method For ReducingHypertension; (2) Appl. No. 61/609,875, filed Mar. 12, 2012, entitledBoost Converter Output Control For Implantable ElectroacupunctureDevice; (3) Appl. No. 61/672,257, filed Jul. 16, 2012, entitled BoostConverter Circuit Surge Control For Implantable ElectroacupunctureDevice Using Digital Pulsed Shutdown; (4) Appl. No. 61/672,661, filedJul. 17, 2012, entitled Smooth Ramp-Up Stimulus Amplitude Control ForImplantable Electroacupuncture Device; and (5) Appl. No. 61/674,691,filed Jul. 23, 2012, entitled Pulse Charge Delivery Control In AnImplantable Electroacupuncture Device.

FIG. 8A shows a functional block diagram of an implantableelectroacupuncture device (IEAD) 100 made in accordance with theteachings disclosed herein. As seen in FIG. 8A, the IEAD 100 uses animplantable battery 215 having a battery voltage V_(BAT). Also includedwithin the IEAD 100 is a Boost Converter circuit 200, an Output Circuit202 and a Control Circuit 210. The battery 115, boost converter circuit200, output circuit 202 and control circuit 210 are all housed within anhermetically sealed housing 124.

As controlled by the control circuit 210, the output circuit 202 of theIEAD 100 generates a sequence of stimulation pulses that are deliveredto electrodes E1 and E2, through feed-through terminals 206 and 207,respectively, in accordance with a prescribed stimulation regimen. Acoupling capacitor C_(c) is also employed in series with at least one ofthe feed-through terminals 206 or 207 to prevent DC (direct current)current from flowing into the patient's body tissue.

As explained more fully below in connection with the description ofFIGS. 15A and 15B, the prescribed stimulation regimen comprises acontinuous stream of stimulation pulses having a fixed amplitude, e.g.,V_(A) volts, a fixed pulse width, e.g., 0.5 millisecond, and at a fixedfrequency, e.g., 2 Hz, during each stimulation session. The stimulationsession, also as part of the stimulation regimen, is generated at a verylow duty cycle, e.g., for 30 minutes once each week.

In one preferred embodiment, the electrodes E1 and E2 form an integralpart of the housing 124. That is, electrode E2 may comprise acircumferential anode electrode that surrounds a cathode electrode E1.The cathode electrode E1, for the embodiment described here, iselectrically connected to the case 124 (thereby making the feed-throughterminal 206 unnecessary).

In a second preferred embodiment, particularly well-suited forimplantable electrical stimulation devices, the anode electrode E2 iselectrically connected to the case 124 (thereby making the feed-throughterminal 207 unnecessary). The cathode electrode E1 is electricallyconnected to the circumferential electrode that surrounds the anodeelectrode E2. That is, the stimulation pulses delivered to the targettissue location (i.e., to the selected acupoint) through the electrodesE1 and E2 are, relative to a zero volt ground (GND) reference, negativestimulation pulses, as shown in the waveform diagram near the lowerright hand corner of FIG. 8A.

Thus, in the embodiment described in FIG. 8A, it is seen that during astimulation pulse the electrode E2 functions as an anode, or positive(+) electrode, and the electrode E1 functions as a cathode, or negative(−) electrode.

The battery 115 provides all of the operating power needed by the EAdevice 100. The battery voltage V_(BAT) is not the optimum voltageneeded by the circuits of the EA device, including the output circuitry,in order to efficiently generate stimulation pulses of amplitude, e.g.,−V_(A) volts. The amplitude V_(A) of the stimulation pulses is typicallymany times greater than the battery voltage V_(BAT). This means that thebattery voltage must be “boosted”, or increased, in order forstimulation pulses of amplitude V_(A) to be generated. Such “boosting”is done using the boost converter circuit 200. That is, it is thefunction of the Boost Converter circuit 200 to take its input voltage,V_(BAT), and convert it to another voltage, e.g., V_(OUT), which voltageV_(OUT) is needed by the output circuit 202 in order for the IEAD 100 toperform its intended function.

The IEAD 100 shown in FIG. 8A, and packaged as described above inconnection with FIGS. 1-7, advantageously provides a tinyself-contained, coin-sized stimulator that may be implanted in a patientat or near a specified acupoint in order to favorably treat a conditionor disease of a patient. The coin-sized stimulator advantageouslyapplies electrical stimulation pulses at very low levels and duty cyclesin accordance with specified stimulation regimens through electrodesthat form an integral part of the housing of the stimulator. A tinybattery inside of the coin-sized stimulator provides enough energy forthe stimulator to carry out its specified stimulation regimen over aperiod of several years. Thus, the coin-sized stimulator, onceimplanted, provides an unobtrusive, needleless, long-lasting, safe,elegant and effective mechanism for treating certain conditions anddiseases that have long been treated by acupuncture orelectroacupuncture.

A boost converter integrated circuit (IC) typically draws current fromits power source in a manner that is proportional to the differencebetween the actual output voltage V_(OUT) and a set point outputvoltage, or feedback signal. A representative boost converter circuitthat operates in this manner is shown in FIG. 8B. At boost converterstart up, when the actual output voltage is low compared to the setpoint output voltage, the current drawn from the power source can bequite large. Unfortunately, when batteries are used as power sources,they have internal voltage losses (caused by the battery's internalimpedance) that are proportional to the current drawn from them. Thiscan result in under voltage conditions when there is a large currentdemand from the boost converter at start up or at high instantaneousoutput current. Current surges and the associated under voltageconditions can lead to undesired behavior and reduced operating life ofan implanted electro-acupuncture device.

In the boost converter circuit example shown in FIG. 8A, the battery ismodeled as a voltage source with a simple series resistance. Withreference to the circuit shown in FIG. 8A, when the series resistanceR_(BAT) is small (5 Ohms or less), the boost converter input voltageV_(IN), output voltage V_(OUT) and current drawn from the battery,I_(BAT), typically look like the waveform shown in FIG. 9A, where thehorizontal axis is time, and the vertical axis on the left is voltage,and the vertical axis of the right is current.

Referring to the waveform in FIG. 9A, at boost converter startup (10ms), there is 70 mA of current drawn from the battery with only ˜70 mVof drop in the input voltage V_(IN). Similarly, the instantaneous outputcurrent demand for electro-acupuncture pulses draws up to 40 mA from thebattery with an input voltage drop of ˜40 mV.

Disadvantageously, however, a battery with higher internal impedance(e.g., 160 Ohms), cannot source more than a milliampere or so of currentwithout a significant drop in output voltage. This problem is depictedin the timing waveform diagram shown in FIG. 9B. In FIG. 9B, as in FIG.9A, the horizontal axis is time, the left vertical axis is voltage, andthe right vertical axis is current.

As seen in FIG. 9B, as a result of the higher internal batteryimpedance, the voltage at the battery terminal (V_(IN)) is pulled downfrom 2.9 V to the minimum input voltage of the boost converter (˜1.5 V)during startup and during the instantaneous output current loadassociated with electro-acupuncture stimulus pulses. The resulting dropsin output voltage V_(OUT) are just not acceptable in any type of circuitexcept an uncontrolled oscillator circuit.

Also, it should be noted that although the battery used in the boostconverter circuit is modeled in FIG. 8B as a simple series resistor,battery impedance can arise from the internal design, battery electrodesurface area and different types of electrochemical reactions. All ofthese contributors to battery impedance can cause the voltage of thebattery at the battery terminals to decrease as the current drawn fromthe battery increases.

In a suitably small and thin implantable electroacupuncture device(IEAD) of the type disclosed herein, it is desired to use a higherimpedance battery in order to assure a small and thin device, keep costslow, and/or to have low self-discharge rates. The battery internalimpedance also typically increases as the battery discharges. This canlimit the service life of the device even if a new battery hasacceptably low internal impedance. Thus, it is seen that for the IEAD100 disclosed herein to reliably perform its intended function over along period of time, a circuit design is needed for the boost convertercircuit that can manage the instantaneous current drawn from V_(IN) ofthe battery. Such current management is needed to prevent the battery'sinternal impedance from causing V_(IN) to drop to unacceptably lowlevels as the boost converter circuit pumps up the output voltageV_(OUT) and when there is high instantaneous output current demand, asoccurs when EA stimulation pulses are generated.

To provide this needed current management, the IEAD 100 disclosed hereinemploys electronic circuitry as shown in FIG. 10, or equivalentsthereof. Similar to what is shown in FIG. 8B, the circuitry of FIG. 10includes a battery, a boost converter circuit 200, an output circuit230, and a control circuit 220. The control circuit 220 generates adigital control signal that is used to duty cycle the boost convertercircuit 200 ON and OFF in order to limit the instantaneous current drawnfrom the battery. That is, the digital control signal pulses the boostconverter ON for a short time, but then shuts the boost converter downbefore a significant current can be drawn from the battery. Inconjunction with such pulsing, an input capacitance C_(F) is used toreduce the ripple in the input voltage V_(IN). The capacitor C_(F)supplies the high instantaneous current for the short time that theboost converter is ON and then recharges more slowly from the batteryduring the interval that the boost converter is OFF.

In the circuitry shown in FIG. 10, it is noted that the output voltageV_(OUT) generated by the boost converter circuit 200 is set by thereference voltage V_(REF) applied to the set point or feedback terminalof the boost converter circuit 200. For the configuration shown in FIG.10, V_(REF) is proportional to the output voltage V_(OUT), as determinedby the resistor dividing network of R1 and R2.

The switches S_(P) and S_(R), shown in FIG. 10 as part of the outputcircuit 230, are also controlled by the control circuit 220. Theseswitches are selectively closed and opened to form the EA stimulationpulses applied to the load, R_(LOAD). Before a stimulus pulse occurs,switch S_(R) is closed sufficiently long for the circuit side ofcoupling capacitor C_(c) to be charged to the output voltage, V_(OUT).The tissue side of C_(c) is maintained at 0 volts by the cathodeelectrode E2, which is maintained at ground reference. Then, for most ofthe time between stimulation pulses, both switches S_(R) and S_(P) arekept open, with a voltage approximately equal to the output voltageV_(OUT) appearing across the coupling capacitor C_(c).

At the leading edge of a stimulus pulse, the switch S_(P) is closed,which immediately causes a negative voltage −V_(OUT) to appear acrossthe load, R_(LOAD), causing the voltage at the anode E1 to also drop toapproximately −V_(OUT), thereby creating the leading edge of thestimulus pulse. This voltage starts to decay back to 0 volts ascontrolled by an RC (resistor-capacitance) time constant that is longcompared with the desired pulse width. At the trailing edge of thepulse, before the voltage at the anode E1 has decayed very much, theswitch S_(P) is open and the switch S_(R) is closed. This action causesthe voltage at the anode E1 to immediately (relatively speaking) returnto 0 volts, thereby defining the trailing edge of the pulse. With theswitch S_(R) closed, the charge on the circuit side of the couplingcapacitor C_(c) is allowed to charge back to V_(OUT) within a timeperiod controlled by a time constant set by the values of capacitorC_(c) and resistor R3. When the circuit side of the coupling capacitorC_(c) has been charged back to V_(OUT), then switch S_(R) is opened, andboth switches S_(R) and S_(P) remain open until the next stimulus pulseis to be generated. Then the process repeats each time a stimulus pulseis to be applied across the load.

Thus, it is seen that in one embodiment of the electronic circuitry usedwithin the IEAD 100, as shown in FIG. 10, a boost converter circuit 200is employed which can be shut down with a control signal. The controlsignal is ideally a digital control signal generated by a controlcircuit 220 (which may be realized using a microprocessor or equivalentcircuit). The control signal is applied to the low side (ground side) ofthe boost converter circuit 200 (identified as the “shutdown” terminalin FIG. 10). A capacitor C_(F) supplies instantaneous current for theshort ON time that the control signal enables the boost convertercircuit to operate. And, the capacitor C_(F) is recharged from thebattery during the relatively long OFF time when the control signaldisables the boost converter circuit.

An alternate embodiment of the electronic circuitry that may be usedwithin the IDEA 100 is shown in FIG. 11. This circuit is in mostrespects the same as the circuitry shown in FIG. 10. However, in thisalternate embodiment shown in FIG. 11, the boost converter circuit 200does not have a specific shut down input control. Rather, as seen inFIG. 11, the boost converter circuit is shut down by applying a controlvoltage to the feedback input of the boost converter circuit 200 that ishigher than V_(REF). When this happens, i.e., when the control voltageapplied to the feedback input is greater than V_(REF), the boostconverter will stop switching and draws little or no current from thebattery. The value of V_(REF) is typically a low enough voltage, such asa 1.2 V band-gap voltage, that a low level digital control signal can beused to disable the boost converter circuit. To enable the boostconverter circuit, the control signal can be set to go to a highimpedance, which effectively returns the node at the V_(REF) terminal tothe voltage set by the resistor divider network formed from R1 and R2.Alternatively the control signal can be set to go to a voltage less thanV_(REF).

A low level digital control signal that performs this function ofenabling (turning ON) or disabling (turning OFF) the boost convertercircuit is depicted in FIG. 11 as being generated at the output of acontrol circuit 220. The signal line on which this control signal ispresent connects the output of the control circuit 220 with the V_(REF)node connected to the feedback input of the boost converter circuit.This control signal, as suggested by the waveform shown in FIG. 11,varies from a voltage greater than V_(REF), thereby disabling or turningOFF the boost converter circuit, to a voltage less than V_(REF), therebyenabling or turning the boost converter circuit ON.

A refinement to the alternate embodiment shown in FIG. 11 is to use thecontrol signal to drive the low side of R2 as shown in FIG. 12. That is,as shown in FIG. 12, the boost converter circuit 200 is shut down whenthe control signal is greater than V_(REF) and runs when the controlsignal is less than V_(REF). A digital control signal can be used toperform this function by switching between ground and a voltage greaterthan V_(REF). This has the additional possibility of delta-sigmamodulation control of V_(OUT) if a measurement of the actual V_(OUT) isavailable for feedback, e.g., using a signal line 222, to thecontroller.

One preferred embodiment of the circuitry used in an implantableelectroacupuncture device (IEAD) 100 that employs a digital controlsignal as taught herein is shown in the schematic diagram shown in FIG.13A. In FIG. 13A, there are basically four integrated circuits (ICs)used as the main components. The IC U1 is a boost converter circuit, andperforms the function of the boost converter circuit 200 describedpreviously in connection with FIGS. 8B, 10, 11 and 12.

The IC U2 is a micro-controller IC and is used to perform the functionof the control circuit 220 described previously in connection with FIGS.10, 11 and 12. A preferred IC for this purpose is a MSP430G24521micro-controller chip made by Texas Instruments. This chip includes 8 KBof Flash memory. Having some memory included with the micro-controlleris important because it allows the parameters associated with a selectedstimulation regimen to be defined and stored. One of the advantages ofthe IEAD described herein is that it provides a stimulation regimen thatcan be defined with just 5 parameters, as taught below in connectionwith FIGS. 15A and 15B. This allows the programming features of themicro-controller to be carried out in a simple and straightforwardmanner.

The micro-controller U2 primarily performs the function of generatingthe digital signal that shuts down the boost converter to prevent toomuch instantaneous current from being drawn from the battery V_(BAT).The micro-controller U2 also controls the generation of the stimuluspulses at the desired pulse width and frequency. It further keeps trackof the time periods associated with a stimulation session, i.e., when astimulation session begins and when it ends.

The micro-controller U2 also controls the amplitude of the stimuluspulse. This is done by adjusting the value of a current generated by aProgrammable Current Source U3. In one embodiment, U3 is realized with avoltage controlled current source IC. In such a voltage controlledcurrent source, the programmed current is set by a programmed voltageappearing across a fixed resistor R5, i.e., the voltage appearing at the“OUT” terminal of U3. This programmed voltage, in turn, is set by thevoltage applied to the “SET” terminal of U3. That is, the programmedcurrent source U3 sets the voltage at the “OUT” terminal to be equal tothe voltage applied to the “SET” terminal. The programmed current thatflows through the resistor R5 is then set by Ohms Law to be the voltageat the “set” terminal divided by R5. As the voltage at the “set”terminal changes, the current flowing through resistor R5 at the “OUT”terminal changes, and this current is essentially the same as thecurrent pulled through the closed switch M1, which is essentially thesame current flowing through the load R_(LOAD). Hence, whatever currentflows through resistor R5, as set by the voltage across resistor R5, isessentially the same current that flows through the load R_(LOAD). Thus,as the micro-controller U2 sets the voltage at the “set” terminal of U3,on the signal line labeled “AMPSET”, it controls what current flowsthrough the load R_(LOAD). In no event can the amplitude of the voltagepulse developed across the load R_(LOAD) exceed the voltage V_(OUT)developed by the boost converter less the voltage drops across theswitches and current source.

The switches S_(R) and S_(P) described previously in connection withFIGS. 10, 11 and 12 are realized with transistor switches M1, M2, M3,M4, M5 and M6, each of which is controlled directly or indirectly bycontrol signals generated by the micro-controller circuit U2. For theembodiment shown in FIG. 13A, these switches are controlled by twosignals, one appearing on signal line 234, labeled PULSE, and the otherappearing on signal line 236, labeled RCHG (which is an abbreviation for“recharge”). For the circuit configuration shown in FIG. 13A, the RCHGsignal on signal line 236 is always the inverse of the PULSE signalappearing on signal line 234. This type of control does not allow bothswitch M1 and switch M2 to be open or closed at the same time. Rather,switch M1 is closed when switch M2 is open, and switch M2 is closed,when switch M1 is open. When switch M1 is closed, and switch M2 is open,the stimulus pulse appears across the load, R_(LOAD), with the currentflowing through the load, R_(LOAD), being essentially equal to thecurrent flowing through resistor R5. When the switch M1 is open, andswitch M2 is closed, no stimulus pulse appears across the load, and thecoupling capacitors C5 and C6 are recharged through the closed switch M2and resistor R6 to the voltage V_(OUT) in anticipation of the nextstimulus pulse.

The circuitry shown in FIG. 13A is only exemplary of one type of circuitthat may be used to control the pulse width, amplitude, frequency, andduty cycle of stimulation pulses applied to the load, R_(LOAD). Any typeof circuit, or control, that allows stimulation pulses of a desiredmagnitude (measured in terms of pulse width, frequency and amplitude,where the amplitude may be measured in current or voltage) to be appliedthrough the electrodes to the patient at the specified acupoint at adesired duty cycle (stimulation session duration and frequency) may beused. However, for the circuitry to perform its intended function over along period of time, e.g., years, using only a small energy source,e.g., a small coin-sized battery having a high battery impedance and arelatively low capacity, the circuitry must be properly managed andcontrolled to prevent excessive current draw from the battery.

It is also important that the circuitry used in the IEAD 100, e.g., thecircuitry shown in FIGS. 10, 11, 12, 13A, or equivalents thereof, havesome means for controlling the stimulation current that flows throughthe load, R_(LOAD), which load may be characterized as the patient'stissue impedance at and around the acupoint being stimulated. Thistissue impedance, as shown in FIGS. 11 and 12, may typically vary frombetween about 300 ohms to 2000 ohms. Moreover, it not only varies fromone patient to another, but it varies over time. Hence, there is a needto control the current that flows through this variable load, R LOAD.One way of accomplishing this goal is to control the stimulationcurrent, as opposed to the stimulation voltage, so that the same currentwill flow through the tissue load regardless of changes that may occurin the tissue impedance over time. The use of a voltage controlledcurrent source U3, as shown in FIG. 13A, is one way to satisfy thisneed.

Still referring to FIG. 13A, a fourth IC U4 is connected to themicro-controller U2. For the embodiment shown in FIG. 13A, the IC U4 isa magnetic sensor, and it allows the presence of an externally-generated(non-implanted) magnetic field to be sensed. Other types of sensorscould be used, as are known in the art, such as any wireless sensingelement, e.g., a pickup coil or RF detector. When a magnetic sensor isemployed, the magnetic field is generated using an External ControlDevice (ECD) 240 that communicates wirelessly, e.g., through thepresence or absence of a magnetic field, with the magnetic sensor U4. (Amagnetic field is symbolically illustrated in FIG. 13A by the wavy line242.) In its simplest form, the ECD 240 may simply be a magnet, andmodulation of the magnetic field is achieved simply by placing orremoving the magnet next to or away from the IEAD. When other types ofsensors (non-magnetic) are employed, the ECD 240 generates theappropriate signal or field to be sensed by the sensor that is used.

Use of the ECD 240 provides a way for the patient, or medical personnel,to control the IEAD 100 after it has been implanted (or before it isimplanted) with some simple commands, e.g., turn the IEAD ON, turn theIEAD OFF, increase the amplitude of the stimulation pulses by oneincrement, decrease the amplitude of the stimulation pulses by oneincrement, and the like. A simple coding scheme may be used todifferentiate one command from another. For example, one coding schemeis time-based. That is, a first command is communicated by holding amagnet near the IEAD 100, and hence near the magnetic sensor U4contained within the IEAD 100, for differing lengths of time. If, forexample, a magnet is held over the IEAD for at least 2 seconds, but nomore than 7 seconds, a first command is communicated. If a magnet isheld over the IEAD for at least 11 seconds, but no more than 18 seconds,a second command is communicated, and so forth.

Another coding scheme that could be used is a sequence-based codingscheme. That is, application of 3 magnetic pulses may be used to signalone external command, if the sequence is repeated 3 times. A sequence of2 magnetic pulses, repeated twice, may be used to signal anotherexternal command. A sequence of one magnetic pulse, followed by asequence of two magnetic pulses, followed by a sequence of threemagnetic pulses, may be used to signal yet another external command.

Other simple coding schemes may also be used, such as the letters AA,RR, HO, BT, KS using international Morse code. That is, the Morse codesymbols for the letter “A” are dot dash, where a dot is a short magneticpulse, and a dash is a long magnetic pulse. Thus, to send the letter Ato the IEAD 100 using an external magnet, the user would hold the magnetover the area where the IEAD 100 is implanted for a short period oftime, e.g., one second or less, followed by holding the magnet over theIEAD for a long period of time, e.g., more than one second.

More sophisticated magnetic coding schemes may be used to communicate tothe micro-controller chip U2 the operating parameters of the IEAD 100.For example, using an electromagnet controlled by a computer, the pulsewidth, frequency, and amplitude of the EA stimulation pulses used duringeach stimulation session may be pre-set. Also, the frequency of thestimulation sessions can be pre-set. Additionally, a master reset signalcan be sent to the device in order to re-set these parameters to defaultvalues. These same operating parameters and commands may be re-sent atany time to the IEAD 100 during its useful lifetime should changes inthe parameters be desired or needed.

The current and voltage waveforms associated with the operation of theIEAD circuitry of FIG. 13A are shown in FIG. 13B. In FIG. 13B, thehorizontal axis is time, the left vertical axis is voltage, and theright vertical axis is current. The battery in this example has 160 Ohmsof internal impedance.

Referring to FIGS. 13A and 13B, during startup, the boost converter ONtime is approximately 30 microseconds applied every 7.8 milliseconds.This is sufficient to ramp the output voltage V_(OUT) up to over 10 Vwithin 2 seconds while drawing no more than about 1 mA from the batteryand inducing only 150 mV of input voltage ripple.

The electroacupuncture (EA) simulation pulses resulting from operationof the circuit of FIG. 13A have a width of 0.5 milliseconds and increasein amplitude from approximately 1 mA in the first pulse to approximately15 mA in the last pulse. The instantaneous current drawn from thebattery is less than 2 mA for the EA pulses and the drop in batteryvoltage is less than approximately 300 mV. The boost converter isenabled (turned ON) only during the instantaneous output current surgesassociated with the 0.5 milliseconds wide EA pulses.

Another preferred embodiment of the circuitry used in an implantableelectroacupuncture device (IEAD) 100 that employs a digital controlsignal as taught herein is shown in the schematic diagram of FIG. 14.The circuit shown in FIG. 14 is, in most respects, very similar to thecircuit described previously in connection with FIG. 13A. What is new inFIG. 14 is the inclusion of an external Schottky diode D4 at the outputterminal LX of the boost convertor U1 and the inclusion of a fifthintegrated circuit (IC) U5 that essentially performs the same functionas the switches M1-M6 shown in FIG. 13A.

The Schottky diode D5 helps isolate the output voltage V_(OUT) generatedby the boost converter circuit U1. This is important in applicationswhere the boost converter circuit U1 is selected and operated to providean output voltage V_(OUT) that is four or five times as great as thebattery voltage, V_(BAT). For example, in the embodiment for which thecircuit of FIG. 14 is designed, the output voltage V_(OUT) is designedto be nominally 15 volts using a battery that has a nominal batteryvoltage of only 3 volts. (In contrast, the embodiment shown in FIG. 13Ais designed to provide an output voltage that is nominally 10-12 volts,using a battery having a nominal output voltage of 3 volts.)

The inclusion of the fifth IC U5 in the circuit shown in FIG. 14 is, asindicated, used to perform the function of a switch. The other ICs shownin FIG. 14, U1 (boost converter), U2 (micro-controller), U3 (voltagecontrolled programmable current source) and U4 (magnetic sensor) arebasically the same as the IC's U1, U2, U3 and U4 described previously inconnection with FIG. 13A.

The IC U5 shown in FIG. 14 functions as a single pole/double throw(SPDT) switch. Numerous commercially-available ICs may be used for thisfunction. For example, an ADG1419 IC, available from Analog DevicesIncorporated (ADI) may be used. In such IC U5, the terminal “D”functions as the common terminal of the switch, and the terminals “SA”and “SB” function as the selected output terminal of the switch. Theterminals “IN” and “EN” are control terminals to control the position ofthe switch. Thus, when there is a signal present on the PULSE line,which is connected to the “IN” terminal of U5, the SPDT switch U5connects the “D” terminal to the “SB” terminal, and the SPDT switch U5effectively connects the cathode electrode E1 to the programmablecurrent source U3. This connection thus causes the programmed current,set by the control voltage AMPSET applied to the SET terminal of theprogrammable current source U3, to flow through resistor R5, which inturn causes essentially the same current to flow through the load,R_(LOAD), present between the electrodes E1 and E2. When a signal is notpresent on the PULSE line, the SPDT switch U5 effectively connects thecathode electrode E1 to the resistor R6, which allows the couplingcapacitors C12 and C13 to recharge back to the voltage V_(OUT) providedby the boost converter circuit U2.

From the above description, it is seen that an implantable IEAD 100 isprovided that uses a digital control signal to duty-cycle limit theinstantaneous current drawn from the battery by a boost converter. Threedifferent exemplary configurations (FIGS. 10, 11 and 12) are taught forachieving this desired result, and two exemplary circuit designs thatmay be used to realize this result have been disclosed (FIGS. 13A and14). One configuration (FIG. 12) teaches the additional capability todelta-sigma modulate the boost converter output voltage.

Delta-sigma modulation is well described in the art. Basically, it is amethod for encoding analog signals into digital signals orhigher-resolution digital signals into lower-resolution digital signals.The conversion is done using error feedback, where the differencebetween the two signals is measured and used to improve the conversion.The low-resolution signal typically changes more quickly than thehigh-resolution signal and it can be filtered to recover the highresolution signal with little or no loss of fidelity. Delta-sigmamodulation has found increasing use in modern electronic components suchas converters, frequency synthesizers, switched-mode power supplies andmotor controllers. See, e.g., Wikipedia, Delta-sigma modulation.

Use and Operation

With the implantable electroacupuncture device (IEAD) 100 in hand, theIEAD 100 may be used most effectively to treat hypertension by firstpre-setting stimulation parameters that the device will use during astimulation session. FIG. 15A shows a timing waveform diagramillustrating the EA stimulation parameters used by the IEAD to generateEA stimulation pulses. As seen in FIG. 15A, there are basically fourparameters associated with a stimulation session. The time T1 definesthe duration (or pulse width) of a stimulus pulse. The time T2 definesthe time between the start of one stimulus pulse and the start of thenext stimulus pulse. The time T2 thus defines the period associated withthe frequency of the stimulus pulses. The frequency of the stimulationpulses is equal to 1/T2. The ratio of T1/T2 is typically quite low,e.g., less than 0.01. The duration of a stimulation session is definedby the time period T3. The amplitude of the stimulus pulses is definedby the amplitude A1. This amplitude may be expressed in either voltageor current.

Turning next to FIG. 15B, a timing waveform diagram is shown thatillustrates the manner in which the stimulation sessions areadministered in accordance with a preferred stimulation regimen. FIG.15B shows several stimulation sessions of duration T3, and how often thestimulation sessions occur. The stimulation regimen thus includes a timeperiod T4 which sets the time period from the start of one stimulationsession to the start of the next stimulation session. The time period T4is thus the period of the stimulation session frequency, and thestimulation session frequency is equal to 1/T4.

By way of example, one set of parameters that could be used to define astimulation regimen is

-   -   T1=0.5 milliseconds    -   T2=500 milliseconds    -   T3=30 minutes    -   T4=7 days (10,080 minutes)    -   A1=6 volts (across 1 kOhm), or 6 milliamperes (mA)

It is to be emphasized that the values shown above for the stimulationregimen are representative of only one preferred stimulation regimenthat could be used. Other stimulation regimens that could be used, andthe ranges of values that could be used for each of these parameters,are as defined in the claims.

It is also emphasized that the ranges of values presented in the claimsfor the parameters used with the invention have been selected after manymonths of careful research and study, and are not arbitrary. Forexample, the ratio of T3/T4, which sets the duty cycle, has beencarefully selected to be very low, e.g., no more than 0.05. Maintaininga low duty cycle of this magnitude represents a significant change overwhat others have attempted in the implantable stimulator art. Not onlydoes a very low duty cycle allow the battery life to be extended, whichin turn allows the IEAD housing to be very small, which makes the IEADideally suited for being used without leads, thereby making itrelatively easy to implant the device at the desired acupuncture site,but it also limits the frequency and duration of stimulation sessions.Limiting the frequency and duration of the stimulation sessions is a keyaspect of applicants' invention because it recognizes that sometreatments, such as treating hypertension, are best done slowly andmethodically, over time, rather than quickly and harshly using largedoses of stimulation (or other treatments) aimed at forcing a rapidchange in the patient's condition. Moreover, applying treatments slowlyand methodically is more in keeping with traditional acupuncture methods(which, as indicated previously, are based on over 2500 years ofexperience). In addition, this slow and methodical conditioning isconsistent with the time scale for remodeling of the central nervoussystem needed to produce the sustained therapeutic effect. Thus,applicants have based their treatment regimens on theslow-and-methodical approach, as opposed to the immediate-and-forcedapproach adopted by many, if not most, prior art implantable electricalstimulators.

Once the stimulation regimen has been defined and the parametersassociated with it have been pre-set into the memory of themicro-controller circuit 220, the IEAD 100 needs to be implanted.Implantation is a simple procedure, and is described above in connectionwith the description of FIGS. 1A and 1B.

For treating hypertension, the specified acupoint at which the EAstimulation pulses should be applied in accordance with a selectedstimulation regimen is at least one of the following acupoints: PC5 orPC6 in the right or left wrist; or ST36 or ST37 in the left or rightleg, just below the knee.

After implantation, the IEAD must be turned ON, and otherwisecontrolled, so that the desired stimulation regimen may be carried out.In one preferred embodiment, control of the IEAD after implantation, aswell as anytime after the housing of the IEAD has been hermeticallysealed, is performed as shown in the state diagram of FIG. 16. Eachcircle shown in FIG. 16 represents a “state” that the micro-controllerU2 (in FIG. 13A or 14) may operate in under the conditions specified. Asseen in FIG. 16, the controller U2 only operates in one of six states:(1) a “Set Amplitude” state, (2) a “Shelf Mode” state, (3) a “TriggeredSession” state, (4) a “Sleep” state, (5) an “OFF” state, and an (6)“Automatic Session” state. The “Automatic Session” state is the statethat automatically carries out the stimulation regimen using thepre-programmed parameters that define the stimulation regimen.

Shelf Mode is a low power state in which the IEAD is placed prior toshipment. After implant, commands are made through magnet application.Magnet application means an external magnet, typically a small hand-heldcylindrical magnet, is placed over the location where the IEAD has beenimplanted. With a magnet in that location, the magnetic sensor U4 sensesthe presence of the magnet and notifies the controller U2 of themagnet's presence.

From the “Shelf Mode” state, a magnet application for 10 seconds (M.10s) puts the IEAD in the “Set Amplitude” state. While in the “SetAmplitude” state, the stimulation starts running by generating pulses atzero amplitude, incrementing every five seconds until the patientindicates that a comfortable level has been reached. At that time, themagnet is removed to set the amplitude.

If the magnet is removed and the amplitude is non-zero (M∧A), the devicecontinues into the “Triggered Session” so the patient receives theinitial therapy. If the magnet is removed during “Set Amplitude” whilethe amplitude is zero (M∧Ā), the device returns to the Shelf Mode.

The Triggered Session ends and stimulation stops after the session time(T_(S)) has elapsed and the device enters the “Sleep” state. If a magnetis applied during a Triggered Session (M), the session aborts to the“OFF” state. If the magnet remains held on for 10 seconds (M.10 s) whilein the “OFF” state, the “Set Amplitude” state is entered with thestimulation level starting from zero amplitude as described.

If the magnet is removed (M) within 10 seconds while in the OFF state,the device enters the Sleep state. From the Sleep state, the deviceautomatically enters the Automatic Session state when the sessioninterval time has expired (T_(I)). The Automatic Session deliversstimulation for the session time (T_(S)) and the device returns to theSleep state. In this embodiment, the magnet has no effect once theAutomatic Session starts so that the full therapy session is delivered.

While in the Sleep state, if a magnet has not been applied in the last30 seconds (D) and a magnet is applied for a window between 20-25seconds and then removed (M.20:25 s), a Triggered Session is started. Ifthe magnet window is missed (i.e. magnet removed too soon or too late),the 30 second de-bounce period (D) is started. When de-bounce is active,no magnet must be detected for 30 seconds before a Triggered Session canbe initiated.

The session interval timer runs while the device is in Sleep state. Thesession interval timer is initialized when the device is woken up fromShelf Mode and is reset after each session is completely delivered. Thusabort of a triggered session by magnet application will not reset thetimer, the Triggered Session must be completely delivered.

The circuitry that sets the various states shown in FIG. 16 as afunction of externally-generated magnetic control commands, or otherexternally-generated command signals, is the micro-controller U2 (FIG.14), the processor U2 (FIG. 13A), or the control circuit 220 (FIGS. 10,11 and 12). Such processor-type circuits are programmable circuits thatoperate as directed by a program. The program is often referred to as“code”, or a sequence of steps that the processor circuit follows. The“code” can take many forms, and be written in many different languagesand formats, known to those of skill in the art. Representative “code”for the micro-controller U2 (FIG. 14) for controlling the states of theIEAD as shown in FIG. 16 is found in Appendix C.

The preceding description has been presented only to illustrate anddescribe some embodiments of the invention. It is not intended to beexhaustive or to limit the invention to any precise form disclosed. Manymodifications and variations are possible in light of the aboveteaching. Thus, while the invention(s) herein disclosed has beendescribed by means of specific embodiments and applications thereof,numerous modifications and variations could be made thereto by thoseskilled in the art without departing from the scope of the invention(s)set forth in the claims.

What is claimed is:
 1. A method of treating hypertension, comprising:generating, by an implantable stimulator, stimulation sessions at a dutycycle that is less than 0.05, wherein the duty cycle is a ratio of T3 toT4, each stimulation session included in the stimulation sessions has aduration of T3 minutes and occurs at a rate of once every T4 minutes,and the implantable stimulator comprises a central electrode of a firstpolarity centrally located on a first surface of a housing of theimplantable stimulator and an annular electrode of a second polarity andthat is spaced apart from the central electrode; and applying, by theimplantable stimulator, the stimulation sessions by way of the centralelectrode and the annular electrode to a location associated with thehypertension and within the patient.
 2. The method of claim 1, whereinthe implantable stimulator is powered by a rechargeable battery.
 3. Themethod of claim 2, further comprising receiving, by the implantablestimulator from an external controller, a power signal configured torecharge the rechargeable battery.
 4. The method of claim 1, wherein theimplantable stimulator is powered by a primary battery.
 5. The method ofclaim 4, wherein the primary battery has an internal impedance greaterthan 5 ohms.
 6. The method of claim 1, wherein the housing of theimplantable stimulator is coin-sized and coin-shaped.
 7. The method ofclaim 1, wherein the annular electrode is located on the first surfaceof the housing.
 8. The method of claim 1, wherein the annular electrodecomprises a ring electrode located around a perimeter edge of thehousing.
 9. The method of claim 8, wherein the annular electrodecomprises a plurality of electrode segments each having the secondpolarity and spaced apart from each other in a circumferential patternaround the central electrode.
 10. The method of claim 1, wherein T3 isat least 10 minutes and less than 60 minutes, and wherein T4 is at least1440 minutes.
 11. The method of claim 1, wherein: a lead is attached tothe implantable stimulator; and the applying the stimulation sessionsfurther comprises applying one or more of the stimulation sessions byway of a plurality of electrodes located on the lead.
 12. A method oftreating hypertension, comprising: generating, by an implantablestimulator configured to be implanted beneath a skin surface of apatient, stimulation sessions at a duty cycle that is less than 0.05,wherein the duty cycle is a ratio of T3 to T4, and each stimulationsession included in the stimulation sessions has a duration of T3minutes and occurs at a rate of once every T4 minutes; and applying, bythe implantable stimulator in accordance with the duty cycle, thestimulation sessions to a location associated with the hypertension andwithin the patient.
 13. An implantable stimulator, comprising: ahousing; a central electrode of a first polarity and centrally locatedon a first surface of the housing; an annular electrode of a secondpolarity and that surrounds the central electrode on the first surfaceof the housing, the annular electrode being spaced apart from thecentral electrode; and pulse generation circuitry located within thehousing, the pulse generation circuitry configured to generatestimulation sessions at a duty cycle that is less than 0.05, and applythe stimulation sessions to a location associated with the hypertensionand within a patient by way of the central electrode and the annularelectrode; wherein the duty cycle is a ratio of T3 to T4, and eachstimulation session included in the stimulation sessions has a durationof T3 minutes and occurs at a rate of once every T4 minutes.
 14. Theimplantable stimulator of claim 13, further comprising a rechargeablebattery within the housing and configured to provide power to the pulsegeneration circuitry.
 15. The implantable stimulator of claim 14,further comprising a receiver circuit within the housing and configuredto receive, from an external controller, a power signal configured torecharge the rechargeable battery.
 16. The implantable stimulator ofclaim 13, further comprising a primary battery within the housing andconfigured to provide power to the pulse generation circuitry.
 17. Theimplantable stimulator of claim 16, wherein the primary battery has aninternal impedance greater than 5 ohms.
 18. The implantable stimulatorof claim 13, wherein the housing of the implantable stimulator iscoin-sized and coin-shaped.
 19. The implantable stimulator of claim 13,wherein the annular electrode is located on the first surface of thehousing.
 20. The implantable stimulator of claim 13, wherein the annularelectrode comprises a ring electrode located around a perimeter edge ofthe housing.